Luthier tool, 13" precision straightedge for checking relief on guitar setup

TECHNOFRET 13" PRECISION STRAIGHT-EDGE

Why a 13" straightedge, you may ask ?

Well, when you are setting up a guitar in a professional manner, you need to set some relief in the fretboard, and this is best accomplished by using a dedicated precision straight edge and feeler gauges. You lay the straightedge along the frets between the first fret and whichever fret the trussrod begins to exert force, which is normally the 12th or 14th fret. You then measure the gap at the 7th fret, which could be anything from zero to .010", (or even more for really heavy pickers), and adjust the trussrod accordingly.

The reason why this TECHNOFRET straight edge is 13" is because that is the one length which will both span  the first and 14th frets of a guitar with a 25.625"  scale (as in some Guilds) , and at the same time  will also span the first and 12th fret of a  guitar with a 24.75" scale (as in many  Gibsons). These are the two extremes you are likely to come across, the straightedge will cover all the combinations in between. Note that a conventional 12" rule will not span the first and 14th frets on guitar with a 25.5" scale.

The pic below shows the straightedge spanning the 1st and 14th frets of a 25.5" scale. ( Strings removed for this pic, obviously in practice you would have the strings on and tuned up to pitch). 

The next pic shows the straightedge spanning the 1st and 12th frets of a 24.75" scale acoustic. Note how the straightedge touches the nut, stops just short of the 13th fret, and also fits neatly between the strings.  

These pics above, due to camera foreshortening, show the straightedge as being almost "pointed" . The pic below shows the true shape.

The straightedge is lightweight, precision ground and lapped from high grade aluminium, and will prove to be an invaluable accessory in the workshop of any guitar tech or luthier. Forget about the crudely inefficient method of trying to measure the gap using a string held down on the 1st and 14th, it never gives an accurate reading. The TECHNOFRET 13" precision straightedge  is the tool for the job.