Negative readings happen when either:
1. The transducers are installed backwards, ie the upstream and downstream transducers are swapped OR
2. The meter needs to be zero calibrated. If you see positive flows most of the time but “negative creep” that’s a good indicator that a zero calibration is required. Zero calibration is started using M42 (Menu 42) and don’t forget to SAVE SETTINGS after zero calibration using M26 (Menu 26).
M37 (Menu 37) is used to reset the totalizers