Spanners.... Do you have access to KLM's Boeing MM? Their 400's have the W&B System fitted (some of them at least). The system operates on strain sensors in the axles(nose wheel) and strain sensors in the bogeys(horizontal section) of the main gear. They measure the bending of the axles and bogeys.
A computer in the MEC does all the number crunching (Another input to the system is a dedicated pitch sensor (for sensing aircraft attitude). The system is mentioned in Chapter 31-41, I believe.
Cheers.
Q.