Okay,
I’m going step in here because this is a recipe for disaster!
Programming an unknown amount of fuel on a digital gauge is pure madness and stupidity!!!
If you own a boat this size pony up and buy some jerry cans (or a tote) and defuel it completely. Then fill it with a known quantity of fuel and program/calibrate your gauge that way. If you have saddle tanks or depending on your filler arrangement you could even make a dipstick for cheap insurance.
Guessing, and running out of gas is a very good way to ruin boating or to be serious a fatality!
You can even put the gas back in afterwards, defuel in the wintertime or prolonged storage and makes the circus of filling a boat at the pumps a thing of the past.
There was a reason nobody responded to this post.