These unique guitar fretboard maps are designed to work on Acoustic guitars and Electric guitars that have a 25" to 25.5" scale length, and Bass guitars that have a 34" scale length.
These instructions also apply to Bass guitar.
To determine your instruments scale length, measure from the fretboard side of the nut to the body side of the bridge stop. Try to take the measurement inbetween the third and fourth strings, right down the middle of the fretboard. Usually the nut is a white piece of bone or acrylic that is at the very top of your guitar fretboard where the strings start over the fretboard. It has little grooves filed in it to "cradle" the strings. The bridge is at the other end of the strings. On an Acoustic guitar the bridge is usually made of wood and has a bone or acrylic "saddle" fitted in it that the strings go over. On an Electric guitar the bridge is usually metal and has small adjustment screws and springs and things. Acoustic electrics can have combinations of both. What you are measuring is the effective vibrating (scale) length of the strings.
Another method is to measure from the fretboard side of the nut to the middle of the twelfth fret wire and then multiply that number by two.