Nightcruzer

I have recently acquired a set of replacement digital gauges for my 1983 TA from a now defunct company called 2001 Technologies Corp. The gauges came with instructions but they are not that clear.
All the gauges, Oil, Elec, Speedo and Tach have a minimum of two adjustment "*****" on the circuit board. One is Zero and the other is Gain. The H20 has two adjustment *****, hot and cold. Fuel is empty or full.
My questions are:
What does gain and zero mean?
What is the proper adjustment process for these gauges?
Does the car have to be actually running to set H20 cold or just power on?
There are only detailed instructions for the fuel gauge.
I've attached partial pics of pages 4 and 5 of the instruction sheet for reference.

Any guidance is appreciated. Thanks.