Excellent suggestion. I need to do that as this trigged a yes its the orignal battery light.
As for the use, you have to play with it.
Start with the basics and do one shot at a time to get a feel for it.
If not a logger type then you need to log each shot. If its a logger than you can shoot strings.
Those will give you the velocity of each shot, you can see what the average was and the standard and extreme deviations. That tells you a lot about ho consistent your loads are.
If the load goes no linear (velocity does not increase per the listed increases) then its your indicator that you have gone too far pressure wise.
Your initial velocity may not match what the books says, but if the book says you increase the power by 1 gr and you get a 50 FPS increase, your load should match that pretty closely (average).