(Another) Intonation Question…

WebParrot (s2)

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[ Concluding Post by OP ... see #56 Resolved ]

Sometimes having good tools to measure parameters can be damaging to ones’ mental health.

I’m reminded of an observation by a favorite college professor, “ I didn’t know I was poor as a kid until I took Economics in college!” Now that I can 'measure' my instruments tuning, the rabbit hole is enlarged...

My two “issues” have to do 1) with being in tune further up the fretboard, and 2) what I can best call a “thunk funk."

Three ‘ukes: 1- Fender Montecito (tenor); 2- Romero Creations Replica (Spruce/Mahogony tenor); 3-Romero ST Concert (spruce top/laminate body).

For all three instruments I used a Korg TM-60 for initial open string tuning (analog needle gauge with digital numeric display) and used the iOS App n-Track Tuner to measure the hz/cent variations. [FWIW, the App matched the Korg for the initial open string tuning.] All strings on each ‘uke have settled.

Starting with the STC, Worth strings (BL-lights). Open strings tuned gCEA to within ‘hundredths’ Hz on the initial pluck, slowly fading slightly flat after about 3 seconds. As I go up the fretboard things start going flat. Depending on the string, flat by 6-9 Cent. By the time I get to the 12th fret, flatness ranges from 16-27 Cent.

Initial setup was done by UkeRepublic. Action: 1st fret 1.0+; 12th fret 2.8 with the first fret being about 0.5mm high. A few individual frets are very slightly low at 3-4 sting locations, but no buzzing. In don’t think the setup included dressing the frets as some of the edges were a little rough as well and the included Romero strings were nicked near the saddle. The saddle on the g string also had a slight groove (you could hear a click when the string was moved from side to side. Finally, the bridge is set at the proper height and distance (with the 12th within 1 mm of center).

Now with the Romero Replica. GCEA (low G)- I started with Romero’s and switched to Clear Worths that had the same diameters as the Romero’s (I kept the Romero flat wound). I followed the same measuring process and the result was less ‘flatness’ at both the 5th and 12th frets. At the 5th the range was 5-7 Cent flat; at the 12th the range was 7-16 cent.

AND for the Montecito. Same Worth strings as the STC. Same process for measuring… Much better results. Within 5 Cent at the 5th (slightly sharp on the E & A). At the 12th fret the G and A were “remarkable” spot on and the middle two 4-6 Cent!

I understand that keeping intonation ‘close’ with shorter fretboards difficult. But with consistently flat intonation in this larger range I was hoping for advice on improving the deficit. Where do I start to ‘sharpen’ the notes as the scale increases. (obviously I’m keeping the ‘inferior’ Montecito as-is … wink)

The second issue has to do with what can best be described as a ‘thunk or thud-iness’ when moving up the fret board, starting at the 5th fret…. only on the C string.

The open string resonance on both the Romero ‘ukes is wonderful, sustaining for 4,5,6 seconds. But when I get to the 5th through 8-9th fret the sustain drops to about 2 seconds and it just sounds ‘dead’. It sounds similar to having your shirt sleeve touching the string ( it isn’t ). There is sufficient clearance at the next fret and I’m careful to press the string at either the middle or closer to the fret with the same thunk. Interestingly, the sustain starts to increase as I continue to move up the fretboard.

Any ideas? FWIW, I don’t get the same result when I play my grandson’s Enya HPL Soprano and Concert models.

Thanks for “listening” … here’s hoping for some ideas.

Stu
 
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You're definitely going down the rabbit hole. All my ukes are off at the 12th, but I decided not to be concerned, just have fun playing. I'm not a professional who records, unless you are, why worry about it? I've heard of people have the bridge moved, but a different set of strings will require that again. The only adjustable uke bridge I've seen is the TunaUke that Lanikai uses where each string sits on a small saddle that can be slid forward and back, but height to lower the action requires sanding like any other saddle.


This is Michael Kohan in Los Angeles, Beverly West near the Beverly Center
9 tenor cutaway ukes, 5 acoustic bass ukes, 11 solid body bass ukes, 9 mini electric bass guitars (Total: 34)

• Donate to The Ukulele Kids Club, they provide ukuleles to children in hospital music therapy programs. www.theukc.org
• Member The CC Strummers: YouTube: www.youtube.com/user/CCStrummers/video, Facebook: www.facebook.com/TheCCStrummers
 
You might try a wound C string to help with the thud.
 
Ok, you can walk away now or go further down the rabbit hole (its fun, honestly). It's time to measure your instrument's with a rule rather than just a tuner.

Nominally your instruments have TOO much compensation at one end of the other which leads the intonation to go flat which is opposite to the usual error in ukuleles of not having enough compensation which leads intonation to go sharp.

Lets talk tenor to start with and a nominal 17" scale length. In a World of "perfect" strings (which don't exist) the distance from inside the nut to where the strings contact the saddle would be exactly 17" and the centre of the 12th fret would be exactly half way at 8 1/2" and every note would play in tune. Now in reality strings are too stiff to vibrate exactly as theory predicts so what happens is that notes go sharp as you fret up the neck. To correct this ukuleles/guitars/all fretted and stringed instruments have saddle compensation making the actual scale length longer than the nominal/theoretical scale length which flattens the note and corrects for the tendency to go sharp.

The amount of compensation at the saddle needs to be reasonably precise. Now we need to talk about the positioning of the nut which also impacts the intonation of the instrument. If the nut is too far away from the 1st fret than it should be then the intonation will go sharp. If the nut is closer to the 1st fret than it should be then the intonation will go flat. A "tiny" bit of nut compensation (nut closer to frets than theory) can be good but just a tiny bit.

One of the most common errors you see in mass manufactured/cheap ukuleles is that they have no saddle compensation (why manufacturers don't know this stuff is beyond me) so they always go sharp.
Your problem is that you have too much compensation at one end or the other or both.

Start by laying a rule down the fretboard from inside the nut to the saddle and comparing the distance from inside the nut to centre of the 12th fret to the distance from inside the nut to the saddle contact point.
How much compensation do you have?
How does the measured distance from inside the nut to centre of the 12th fret compare to the theoretical distance from inside the nut to centre of the 12th fret? THis should be 8 1/2" on a tenor ukulele however it can get more complicated than that as the instrument may have been built in metric rather than imperial.

17" converts to 431.8mm. Tenors are still commonly built to this scale length although sometimes they are built to a metric 432mm scale length.
A 15" Concert scale is 381mm although its common to have them built to 382mm metric as well.

Ae you still with me?
 
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Yes! I'm not the OP but I really learned from your post.

Thanks. I'll keep on going.

First we need to measure so we KNOW where the error is. My experience is that if I measure an instrument carefully then I will always find a measurable error if the intonation is out. If the instrument has great intonation then the instrument will measure accurately.

Let me shortcut for a moment and then go back.

If an instrument is reasonable accurate at the low frets and gradually gets worse up the neck then the nut should be correctly placed and the error is in the saddle.
If an instrument is bad over the first few frets and gets better up the neck then its the nut at fault and the saddle is probably right.

In reality its often both that are wrong.
Now sometimes things can get REALLY complicated because the fault MAY be at the nut yet some tech guy tries to fix it by compensating for the error at the saddle.
This happens a LOT and I have a bee in my bonnet about it. Now I've made this very error myself many times so I don't want to be too critical of tech guys and my attitude nowadays is to try my best to teach the theory as best I can.

One example from me is that I own a hand made electric ukulele that was going flat over the low frets and I couldn't set the saddles short enough to fix it. I took the instrument to a shop and had them move the bridge closer. Later on I learn't/realised that it was in fact the nut that was positioned too close and in fact the bridge was just fine where it was originally. Now that I have the nut fixed the saddles need to be back as far as they can go:(

So, before we do ANYTHING, first measure. All over.

So for a 17" Tenor lay a steel rule from inside the nut to over the saddle and note where things are positioned. Is the centre of the 12th fret precisely at 8 1/2"? The saddle should be at 17" plus a little but just how much extra is there?

That's a start.


Now when your REALLY ready to go down the rabbit hole.

To do this really well you must first independently establish the precise scale length that the frets are fretted to. Guessing that its 17" (431.8mm) when its really 432mm isn't close enough. We need to be precise and the way you do this is with the help of Stewart MacDonalds fret position calculator.

https://www.stewmac.com/FretCalculator

What you do is make an educated guess as to the scale length and put the data into the calculator.
Then make some fret to fret distance calculations. Work out the distance from fret 16 to fret 1 and fret 12 to fret 1. You do the calculations to 3 decimal places first and any rounding is done last. Once you have your distances, carefully measure them on the fret board. Are they correct?

I've just been working on some baritones that are nominally 19". They were measuring accurately from inside the nut to the centre of the 12th fret at 9 1/2" so I though it was spot on. Recently I figure that I had better do the right thing and measure them with the help of stewmac. To my surprise they weren't 19" ( 482.6mm) but were actually 482mm.
You need to be this accurate.
 
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Down the rabbit hole indeed. It is all right and proper to stress the need for accuracy in these essential placements, but don't take it too far. IMHO to suggest that we have to work to an accuracy of two tenths of a millimeter is unrealistic.

John Colter.
 
Down the rabbit hole indeed. It is all right and proper to stress the need for accuracy in these essential placements, but don't take it too far. IMHO to suggest that we have to work to an accuracy of two tenths of a millimeter is unrealistic.

John Colter.

Well its up to you of course. For the record a 0.2mm difference to saddle compensation WILL make a difference and is well within the range of adjustments that you could expect a tech to do when fine tuning intonation. The tech may not have measured it with a rule yet they will have likely adjusted it, restrung the instrument and tested it with a tuner. A 0.2mm error in nut placement will have an effect.

My advice to builders and techs is to not try to fix a 0.2mm error at the nut with a 0.2mm adjustment to the saddle. The first step is to know what needs to be adjusted before you start.

It makes a BIG difference.
 
Down the rabbit hole indeed. It is all right and proper to stress the need for accuracy in these essential placements, but don't take it too far. IMHO to suggest that we have to work to an accuracy of two tenths of a millimeter is unrealistic.

John Colter.

Well written Anthony

My few pennth’s worth as a Mechanical Engineer.

Number 1

The Nut has to be right, it is the Datum, the reference from which all measurements are taken.

Screw up the Nut and you screw up the whole scale.

Number 2

Distances between frets have to be accurate and as per the calculator, this should not be an issue during manufacturer.

Number 3

Saddles fitted to the vast majority of Ukes are generally budget items with no easy adjustment to fine tune the string length.

Joe Public may not be able to work to two tenths of a millimeter (roughly 8 thousandths of an inch) but a good Tech should be able to and certainly the fully adjustable saddle that I have on my Risa Uke can enable adjustment to far less than two tenths of a millimeter.
 
OP - First reply.
I'm honored by the number of replies and the wisdom you've shared. To @anthonyg you've fulfilled my need-to-know and delighted my curiosity. I'll add to this reply shortly ( Currently 9:30 am CST ). I've made a number of measures to the three instruments and the results dovetail ( not rabbit tail ) to what he's shared in his diatribe.

If I have one regret is that I failed to make one point clear. My interests have to do with asking "why" and not looking for perfection. It's clear from reading the dozens of posts on intonation that there is no 'perfect.' Two 'ukes from quality makers that received "full" setups, and one from a mass production vendor with no setup. The later doesn't display the large range of increasing "flatness" of the former. I am/was curious as to why the flatness occurs, and from it, what could be changed to improve the two to the level of the Montecito. While I'm not in the OCD universe, over the decades I've learned that failing to look down a rabbit hole can make you blind to understanding, alternatives, and solutions. :) Thanks again, more detail info to follow.
Stu
 
I want to give props to anthonyg for the concise and detailed information....very well explained.

No matter how far down the rabbit hole you want to go (as that is a personal choice) you have provided a great deal of experiential knowledge and insight to getting folks where they want to be.
I personally don't mind all the details and accuracy. The way I have approached ukulele building (or any instrument I make) is that knowing that perfection is unobtainable, means I need to be as accurate as I can to get as close as I can when it all comes together. As a minuscule amount here and there can in some cases add up to a problem later on.

A specific detail may make no discernible difference to one person but that does not mean it is the same for another. As an example: My son has been apprenticing as a sound engineer for a while now and he is recording a bunch of songs I have written over the years to keep his gears rolling in between gigs. We will be listening to playback and he hears and notices things that I cannot even hear. So what does not matter to me, bothers him. So, I just have him do what he needs to do to feel good about it and everyone wins.

So I would say that if you want to be close and do not care about going all the way because you cannot tell the difference, no problem, just do it to your liking (or ability) and round off that 0.2mm difference. It will definitely be better than the crappy factory non-set up you get with most cheap ukuleles. But if you want to go all the way, then get as accurate as you can all the way through.

However, I think the more important point is that if you round off the 0.2mm on your first measurement you may miss the fact that the problem is at the nut and not the saddle or a fret that was misplaced, etc.. So I would say that the main point is that you take as accurate of a measure as one can of all these aspects before you break out a file..... I too have learned this one the hard way in the past.

No matter what you choose the point is to be happy with the results and that is what matters.
 
OP here - followup ( 3:40 CST )
Intonation Measures.
Part two.
Using the StewMac calculator suggested by “anthonyg” (thank you!), a digital caliper, and a metric scale 400mm ruler I took measurements
1)of the scale,
2)at the twelfth fret, plus;
3)measurements from the nut to frets 1,2,3,4,5,6,7. (using the digital caliper)
4)measurements fret-to-fret at nut-1, 4-5, 6-7, 9-10, 11-12 (using the digital caliper)

Both the Romero STC and Replica have “factory” compensated saddles for the C and E strings, set back slightly more than 1.0 mm.

First, the Montecito tenor. (gCEA uncompensated saddle) Scale: 381+ 12th Fret 215.5
Fret measurements up to the 7th fret were within 0.5% of the StewMac Calculator
Fret measurements BETWEEN frets were generally over 0.5mm - very close

Second, the Romero Replica tenor 18 frets (compensated saddle for the C and E strings)
Scale length for the G and A - non-compensated strings 433mm with 12th fret at 215.5
Scale length for the C and E - compensated strings 434.5mm with 12th fret at same 215.5
Nut to 1st fret was short by 0.3mm ( 24.302 v. 23.975 )
Nut to 5th fret was short by 0.87mm ( 108.993 v. 108.12 )
Nut to 7th fret was short by 1.15mm ( 144.506 v. 143.36 )
Difference in fret-to-fret measures were scattered. Three were over .25, three minimally below zero.

Third, the Romero STC As with the Replica, it has a gCEA uncompensated saddle. Promoted as concert scale on a tenor body and 22” in total length. The fret board scale is 380mm (g and A), and 381mm (C and E).
Scale at the 12th fret is 187.5mm and the scale is 15 ( and 1/2 ) frets (half the 16th fret is removed over the sound hole. When I tried to use the StewMac calculator the results didn’t make sense so I didn’t go into comparative measurements.

With both the Romero’s having bridges/saddles exceeding the half-way measures to the long side, intonation going flat when moving up the fretboard makes sense. This exercise has helped me understand the relationship, especially when the number support the very helpful description that “anthonyg” detailed (thank you AGAIN).

I highly doubt that I would do anything with the Replica. I rarely play that far up on a tenor. But I’ll have to think further whether to have something done with the STC. It’s noticeably flat, even to my ‘senior’ ears. When I have more time I’m going to do the same nut-to-fret measurements on it to see how it differs from another concert that I have (which doesn’t have similar issues).

Thanks again to those who contributed to my journey :) I hope others can use the information for their better understanding as well. And if anyone has some additional thoughts, please share. This is a great forum to learn.
Stu
 
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Just to make my position clear, I have no issue with AnthonyG's explanation of the relationships of nut, frets, and saddle, and the need for compensation at the saddle. All that was clear and concise, and will be very helpful to anyone who has not studied these matters.

What I take issue with is the advice to measure these relationships with a steel rule, expecting to do so to an accuracy of two tenths of a millimeter. Tell me - how thick are the markings on your steel rule?

My eyesight is pretty good. I reckon I can measure to about of one third of a millimeter, using a steel rule, but less that a quarter of a millimeter?

No way!

John Colter.
 
I'm glad I could help and those are some impressive measurements.

I should clarify things as you've probably done more measurements than you need to do.
What all those nut to fret measurements have shown is that the nut IS too close and its a matter of filing it or shimming it back.

You only really need to do one nut to fret measurement and thats the centre of the 12th fret to inside the nut. For this measurement to make sense though you first MUST know the precise scale length that the frets are fretted for.

TO do this I'm recommending calculating the 1st fret to 12th fret and 1st fret to 16th fret distances and then measuring them to see if they're accurate. If there a little out then adjust the figures on the calculator and do it again. You most definitely will have variances between a nominal Imperial scale in inches and its closest metric equivalent.

Is a Tenor 17" (431.8mm) or metric 432mm. Is a Concert 15" (381mm) or 382mm. Is it 19" (482.6mm) or just 482mm.
When you KNOW what the frets are then you can just measure from inside the nut to the centre of the 12th fret.
More measurements can be used to see how accurate all the frets are though.

When the nut is placed spot on in relation to the frets then 2mm +/- a fraction of saddle compensation is pretty good. A tiny bit of compensation at the nut can be good (0.3mm closer approx) but if's going flat its going flat. If so then file it back.

If the material on the nut or saddle is there in the right spot then it can be adjusted. Its a damn sight harder to "adjust" into thin air.

EDIT. Also I should add.My experience is that a 1mm gap from the nominal scale length to the leading edge of the saddle is right. The needed saddle compensation should fall somewhere on the saddle material. Its a matter of fine tuning. If the required compensation isn't falling on that saddle then look for an error in the nut.
 
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Just to make my position clear, I have no issue with AnthonyG's explanation of the relationships of nut, frets, and saddle, and the need for compensation at the saddle. All that was clear and concise, and will be very helpful to anyone who has not studied these matters.

What I take issue with is the advice to measure these relationships with a steel rule, expecting to do so to an accuracy of two tenths of a millimeter. Tell me - how thick are the markings on your steel rule?

My eyesight is pretty good. I reckon I can measure to about of one third of a millimeter, using a steel rule, but less that a quarter of a millimeter?

No way!

John Colter.


John, I agree that these measurements are hard to make accurately and taking centre fret to centre fret measurements is particularly difficult. This in no small way is why I am specifically instructing people to do the calculations first based on an educated guess and then lay the rule on the frets. Measuring the frets first and then trying to compare them to the stewmac calculator's data will give nonsense results.

You will see a difference though in a 0.2mm adjustment. One will look closer than the other. The difference between 482.6mm and 482mm was easy to spot.
Also definitely do at least two LONG measurements. Trying to measure from fret 1 to fret 3 will also give nonsense results.
 
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My final notes:
Just some clarification on my measurement process. First, I used a digital caliper for the nut-to-fret for frets 1 thru 9. To get the center value for the frets, I sampled the thickness of a few frets (using the caliper) and divided the value by 2. I then measured from the nut to the nut-side of each fret, then added the half-value to get the distance to center. For the fret-to-fret values I simply measured top edge to top edge using the presumption that the frets were near similar thickness (edge to edge = center to center).

As for the remaining measurements I used an etched Machinists’ metric ruler, certified accurate to 0.5mm ( Start brand ). Where a value ‘mark’ fell between the etched markings I simply interpolated the value to 0.25. Any values not in multiples of those are a result of adding the half-fret measurements to the ruler reading.

I’ve attached a scanned copy of my worksheet for the Romero STC. If I’ve correctly understood the responses here, the values at the 12th fret are larger than they should be and probably causing the “flat” Cent reading and noticeable (to my ear) out of tune. While it might seem I’ve taken this to an unnecessary level to affirm that conclusion :) …. I wanted to learn a lot and truly did! Thanks to everyone for sharing their knowledge and opinions.
(ps-I’ve also learned to ‘author’ my replies in a word processor and “paste” the reply into the forum. It doesn’t like me and has bumped me out without saving!! grrrr)

View attachment 118223
 
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My final notes:
Just some clarification on my measurement process. First, I used a digital caliper for the nut-to-fret for frets 1 thru 9. To get the center value for the frets, I sampled the thickness of a few frets (using the caliper) and divided the value by 2. I then measured from the nut to the nut-side of each fret, then added the half-value to get the distance to center. For the fret-to-fret values I simply measured top edge to top edge using the presumption that the frets were near similar thickness (edge to edge = center to center).

As for the remaining measurements I used an etched Machinists’ metric ruler, certified accurate to 0.5mm ( Start brand ). Where a value ‘mark’ fell between the etched markings I simply interpolated the value to 0.25. Any values not in multiples of those are a result of adding the half-fret measurements to the ruler reading.

I’ve attached a scanned copy of my worksheet for the Romero STC. If I’ve correctly understood the responses here, the values at the 12th fret are larger than they should be and probably causing the “flat” Cent reading and noticeable (to my ear) out of tune. While it might seem I’ve taken this to an unnecessary level to affirm that conclusion :) …. I wanted to learn a lot and truly did! Thanks to everyone for sharing their knowledge and opinions.
(ps-I’ve also learned to ‘author’ my replies in a word processor and “paste” the reply into the forum. It doesn’t like me and has bumped me out without saving!! grrrr)

View attachment 118223

You've done some great work and I applaud you, however you missing one of my points.
Before this work makes any sense you first must establish the actual scale length of the frets, WITHOUT using the nut as a reference point. This is very important.
Just how did you decide that the nominal scale length was 380mm? Its more likely to be 381mm or 382mm and in this scenario all your figures will be low as they are.

So, first things first. Using the 380mm scale length data, calculate what the distance from fret 1 to fret 16 will be. Calculate what the distance from fret 1 to fret 12 will be.
Do the distances line up or are they short of the mark? Try 381mm and try 382mm doing the calculations again. Which looks closer? It might even be something else.

Yes. These distances are outside the range of your digital callipers so I do understand why your doing it your way but there is method to my madness. You try out a few and one will look right or the closest.

This is importantly the first measurement to make/confirm.
Once the scale is established independently from the nut then its a simple measurement from inside the nut to the centre of the 12th fret to establish the nuts placement.
The work you have done is checking the accuracy of the fretting yet its giving you false data until you have established the correct scale length independently from the nut.

Its all learning yet I have stated multiple times that you need to measure fret 1 to 12 and fret 1 to 16. This is key. This is first.

EDIT: OK, for the record I AM using reading glasses for checking scales and I have a strong set just for getting up close as well. These are cheap reading glasses. Nothing prescription.
 
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My final notes:

(ps-I’ve also learned to ‘author’ my replies in a word processor and “paste” the reply into the forum. It doesn’t like me and has bumped me out without saving!! grrrr)

View attachment 118223

This is sage advise. Apart from losing partly written posts, I have also lost lengthy documents when submitting (not to this forum). Apparently with some forum software, if two posts are submitted simultaneously, one is preferentially accepted and the other may be lost to the 'ether'. This should not happen but it sometimes does .... I have been an unlucky victim on a few occasions now, so if my posts are to be more than a few sentences, I also use a word processor.
 
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FollowUp Clarification (widen your viewing screen for best data layout)

You've done some great work and I applaud you, however you missing one of my points.

Its all learning yet I have stated multiple times that you need to measure fret 1 to 12 and fret 1 to 16. This is key. This is first.
.

:) Your points were not overlooked, but perhaps my cut n’ paste effort failed to include the scale info as intended. I've captured the information, re-measured both the Romeros (see [Note*] ), and presented in a format that makes it easier to compare.
All my measurements are metric. I’ve re-measured both my Romero’s

“actual” nut to saddle measurements for the Romero STC: g-@-380mm C-@-381mm E-@-381mm A-@-380mm
Saddle is a factory compensated (C&E) and I measured from the point on the saddle where the string first breaks over the bridge after emerging from the bridge.

Fret to fret measures:
*Ctr of 1st to 12th frets@ 166.5mm = Ctr 1st to 16th frets@ 205mm => diff 38.5mm
StewMac (381mm) 1-12 = 169.120mm 1-16 = 208.42mm => diff 39.3mm
StewMac (382mm) 1-12 = 169.560mm 1-16 = 208.96mm => diff 39.4mm


“actual” nut to saddle measurements for the Romero Replica RCR: G-@-433mm C-@-434.5mm E-@-434.5mm A-@-433mm Saddle is compensated (C&E) and I measured from the point on the saddle where the string first breaks over the bridge after emerging from the bridge.

Fret to fret measures:
*Ctr of 1st to 12th frets@ 191.5mm = Ctr 1st to 16th frets@ 236.0mm => diff 44.5 mm
StewMac (431.8mm) 1-12 = 191.650mm 1-16 = 236.21mm => diff 44.56mm
StewMac (432.0mm) 1-12 = 191.740mm 1-16 = 236.31mm => diff 44.57mm

So… choosing the StewMac calculator imperial scales for both comparisons ( 15” and 17” respectively ) I compared my original measurements, nut-to-fret, at the 1st, 5th, and 12th frets.

STC (15”) @ Nut to 1st -> 20.97mm 15”scale -> 21.384mm
Nut to 5th -> 93.96mm 15”scale -> 95.573mm
Nut to 12th -> 186.2mm 15”scale -> 190.500mm

RCR(17”) @ Nut to 1st -> 24.00mm 17”scale -> 24.235mm
Nut to 5th -> 108.2mm 17”scale -> 108.316mm
Nut to 12th -> 216.0mm 17”scale -> 215.900mm

With this added clarity :) I’m interested in any supporting conclusions that have become more obvious.
Thanks TONS (metric, of course) for your time and expertise and guidance.

[*Note: Centre to Centre measurements were actually taken from the top edges of the frets with the ruler carefully registered against the edge. All the frets appeared to be similarly crowned so I’m resuming the relative point to point measurements are pretty close!.]
 
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