FCeng84:
I'm curious as to what signal is used in Direct Law to schedule the gain between stick and elevator. What is the source of CG data to effect this scheduling?
Expanding on m39462's comment, on the A330 there are two Fuel Control and Monitoring Computers (FCMC) that control the fuel system. One of the functions of the FCMC is to calculate the aircraft's Gross Weight and Centre of Gravity. That calculation is based on the Zero Fuel Weight and the ZFWCG entered by the crew during pre-flight initialisation of the Flight Management Guidance and Envelope Computers (FMGEC [i.e. the FMC for you Boeing types!]), and the sensed fuel quantity and distribution.
The FMGEC normally uses the GW and CG information calculated by the FCMC. That information is passed on to the Flight Control Primary Computers (FCPC, or 'PRIM'). If both FCMCs fail, the Flight Envelope (FE) part of the FMGEC is also able to compute the GW and CG as a backup.
Simple really (not!!).