Agree with InTransit. In addition, may I suggest the following:
Whilst planning, and having established how much fuel you will depart with, make the top line of your fuel log your
Flight Fuel(Not total FOB) in minutes. You might want to divide the top line into columns representing different tanks depending on your aircraft type, and update your log as you change tanks.
Keep it simple. You don't plan to burn your reserves, so don't let them concern your in-flight calculations (unless of course it becomes a concern !
). Then, as you complete your log at regular intervals, you can compare your
flight fuel remaining in minutes with your planned ETI's. If the fuel guage actually works, Gross Error Check by comparing the guage with your expected FOB per InTransits idea.
Probably many schools of thought. Chat to your instructor / CFI.
Cheers,
Inbound