I found these gauges to be unreliable. On my B47 there are four rods that dip at different levels into the water, and a long rod that reaches the bottom. The PB-42 board "adds up" the voltages from these four sensors, so if one isn't reading properly, you get a spurious reading. I've replaced my gauge with four LEDs, so if a middle sensor is missing, it still gives a sensible reading.
My next plan is to make a duplicate board and replace all the wiring, they use ribbon cable with connectors not suitable for the marine environment.