Brake float
Brake is a float value determined by the percentage of brake application being applied in-sim after any brake force curves are taken into consideration, with 0 being a closed throttle and 1 being fully open.
For the pedal position please see BrakeRaw
Developer Post
ThrottleRaw, BrakeRaw - These show your raw throttle brake inputs before any throttle shaping, brake force curve, or any lift/cuts from the transmission. So you can think of Throttle being a sensor on the throttle body and throttle raw being a sensor on the pedal. This is handy for the Williams since there are so many lifts and cuts you never can tell what is going on.