46 CFR §154.1305

1. (a)Each cargo tank must have at least one liquid level gauging system that is operable:
   1. (1)At pressures up to, and including, the MARVS of the tank; and
   2. (2)At temperatures that are within the cargo handling temperature range for all cargoes carried.
2. (b)Unless the cargo tank has one liquid gauging system that can be repaired and maintained when the tank contains cargo, each cargo tank must have at least two liquid level gauging systems that meet paragraph (a) of this section.
3. (c)Each liquid level gauging system must measure liquid levels from 400 mm (16 in.) or less from the lowest point in the cargo tank, except collection wells, to 100 percent full.