Just how accurate are the 737NG fuel qty indicators anyhow?
I know that each type of system has it's own pros and cons, but per the FAA (for those aircraft built under FAR 25)
§ 25.1553 Fuel quantity indicator.
If the unusable fuel supply for any tank exceeds one gallon, or five percent of the tank capacity, whichever is greater, a red arc must be marked on its indicator extending from the calibrated zero reading to the lowest reading obtainable in level flight.
Having flown the old probe system, I know that pitch and roll angles changed the readings. Also, there was the question of how long ago the system was calibrated.