[Brent Hutto]

You can measure the distance from E-string to E-string at the nut. And you can measure the distance from E-string to E-string at the saddle. On my dred those measurements are 38mm and 56mm (approximately, from memory). Call it 1.50" and 2.20" for convenience.

So the distance from E-string to E-string at the 12th fret will be midway between those two numbers or 1.85".

The distance from E-string to E-string at the 7th fret will be a third of the way between or 1.73".

The distance from E-string to E-string at the 5th fret will be a fourth of the way between or 1.68".

The 3rd fret isn't a harmonic so I don't know the exact ratio but it will work out to somewhere around 1/6 of the distance or 1.62" more or less.

So the point made by Bill and others is correct. That 1-11/16" or 1.8" or 1-3/4" or whatever number isn't really informative. The string spacing on a particular guitar at the top and bottom is what it is. Measure that spacing and the spacings in between fall proportionally. There is no standard for how string spacing relates to nut width.