[charles Tauber]

Originally Posted by zeeway

The scale length of a string is the length of the string available to vibrate, period...the scale length is a bit different on every string

You can redefine the term anyway you wish, as Martin has. Most of the world regards the scale length as the theoretical string length, the one used to calculate the position of the frets.

Unless you are making a "multi-scale length" guitar (including a "fan fret"), the scale length is the same for all strings. What differs is the amount of compensation, giving each string its own actual vibrating string length. Regardless, the scale length remains the same for each string.

So, in designing a guitar, you choose the scale length, which is used in the calculation for fret locations. Then somewhere down the line you compensate the saddle, to get the tuning more exact...which alters the scale length of those strings...which means you should recalculate the fret positions, which means you should....keep chasing your tail.

What most guitar makers/designers do is chose a scale length. The scale length is used to calculate the fret positions. Once calculated, the fret positions are never changed, but, perhaps, for the distance from the nut to the first fret (compensation at the nut).

The saddle is then moved away from the nut to make the actual vibrating string length longer than the scale length. Doing so provides compensation for the increase in pitch caused by depressing the strings against the frets and, for some, some correction of inharmonicity. It is, generally, a once-through process with no chasing of one's tail. (There can be some back and forth if one is optimizing intonation using both nut and saddle compensation.) The scale length and fret positions are not changed.

By using agreed-upon terminology, communication is facilitated. The generally agreed upon terms, and their meanings, is as follows:

Scale length is the theoretical length of the vibrating strings and is used to calculate fret positions.

The actual vibrating string length is the "speaking" length of the actual vibrating string. In practice, the actual vibrating string length is always longer than the scale length.

Compensation, at nut and/or saddle is the amount by which the actual vibrating string length differs from the scale length. When nut compensation is used, the nut/zero fret is moved closer to the first fret decreasing the theoretical distance from nut to first fret given by the scale length. When saddle compensation is used - it universally is used - the breaking point of the string over the saddle is moved away from the nut to increase the actual vibrating string length.