Bass Bridge Installation

[Spector_Ray]

I've been playing bass for over 20 years and I'm just getting around to building my first bass.  I have a Mighty Mite P-bass body that is front routed for standard P pickups and control cavity.  My question is how do I measure for the bridge location? 

 

[Edin]

Simply, distance  from nut to 12th fret must be equal distance 12th fret to the bridge...