I never did set the "three things" on my Trimetric because IMO bank capacity is so variable with temperature. I have a rough idea of what full AH is during particular camping sessions and just use the accumulated AH and that notion of capacity to figure my own percentage SOC.
I cross-check this with the "morning voltage" and can see if they match "within reason." The other cross-check is on recharging, I use the amps per battery as above against the AH reading and voltage to see if they match.
I really like having the Trimetric for seeing what amps are being used/put in and the accumulated AH. I use the voltage read-out too, but could get that with a simple voltmeter before and still can where I want to see it to two decimal places.
I find the several pages of detailed programming into the weeds that the Trimetric will do is just silly when you can't even get a good capacity of the bank to base it all on anyway. Weird.