Originally Posted by
Trevor Davies
The guitar scale length is measured from the fretboard side of the nut to the saddle for the high E string. For the TOM (or any!) bridge the saddles are in a step wise arrangement (see the picture below). The TOM bridge is not parallel to the PUPs to account for the lack of travel (or adjustment) of the saddles.
The actual position of the saddles will depend upon the type of strings used, thickness of the strings used, the height (or action) of the strings from the neck. All these factors will determine the final string length for intonation.
The Science behind it is that when a string is pressed onto a fret (say 12 th), its tension must increase, which increases the frequency of the vibrating string. To compensate for this the string need to be made slightly longer than the scale length. The thicker the string, the greater the change in tension, so the longer the intonation length.
I hope this helps!