"Jim Weir" wrote in message news
I have heard this repeated for quite a while, and I can't find the pertinent
section of the aircraft certification regs. Would you mind posting the chapter
and verse where I can find this requirement?

Jim


It doesn't say that. 23.1337 says the guage must be calibrated (but doesn't give any specific
accuracy). The part that people keep passing around by is the (1), but they ignore the fact
that it comes after "In Addition" . The empty pronouncement just says that the bottom mark
is supposed to be zero usable as opposed to bone dry:

(b) Fuel quantity indication. There must be a means to indicate to the flightcrew members the quantity of
usable fuel in each tank during flight. An indicator calibrated in appropriate units and clearly marked to
indicate those units must be used. In addition:
(1) Each fuel quantity indicator must be calibrated to read "zero" during level flight when the quantity of
fuel remaining in the tank is equal to the unusable fuel supply determined under § 23.959(a);