The scale length of a guitar is the distance from bridge to nut or in the Brian may case the Zero fret to the bridge. The scale length starts where it leaves the zero fret. Not the nut! The nut on Brian Red special guitar is merely a string guide, to keep the strings in place, and to guide them to the tuners.
Brian's scale length is 24 inches, or to people who use millimetres 610 mm. if you measure the scale with a ruler or tape measure 12 inches it comes to the 12th fret on the guitar which is half way on the scale, here you will find the harmonics, if you gently touch and pluck the string, for example B, the harmonic should be B. If you play the string at the 12th fret it should also be B, you can see this on your tuner if you have one.
You can use this method to set up your guitar, its called intonation, if the guitar is not setup correctly or the bridge is in the wrong place it will not play in tune all the way up the neck. When you play the harmonic above the 12th fret and on the 12th, they should both read the strings note its tuned to. Some times it will appear a little sharp or flat. You can sort this problem by adjusting the saddle on the guitar or moving your roller in your BM roller bridge backwards or forwards, increasing or decreasing the scale length, there for adjusting the intonation. If you can get the harmonic and not as close to perfect as possible then your on to a winner..
A question was raised by member Gilmour: where do you position a bridge?
In response to this, your scale length is 24 inches (610 mm) from the middle of your zero fret to the bridge. The bridge on a BM guitar would be 12 inches (305 mm) from the 12th fret. I position the bridge either in the middle of the end of the scale length to have adjustment equal both ways if I need to move the roller, or, I position it towards the front of the bridge so I can have more movement backwards. I would suggest getting your bridge, tape the 6 blocks together as if they were fixed, and test where you best intonation point is, please remember this does change depending on string gauge. Also it's worth trying to get the height of your string action while your have this taped together. When fixing the Bm Roller bridge, I keep it taped together, so I can drill the holes to fix them to the body. You can mount the bridge on the pick-guard, or brass shims. The screws travel through these to fix it to the body.
If it's a stud mounted bridge, that's another story.
While some electric guitarists use a shorter scale instrument to achieve less string tension and easier playability, others see it as an opportunity to get a "thicker" tone utilizing heavier gauge strings.