12 hours ago, downscc said:

There is not much of a reason to use the manual fuel entry on the PERF page in a simulation unless you are using a simulated ground environment

In real life, you would most likely use this if one of your fuel tank quantity indication systems had failed.There is an MEL which applies. It has some rather critical procedures for making sure the tank has been fuelled to the correct quantity before flight (There are "dipsticks" in the tanks for checking fuel quantity manually)

Cheers

11 hours ago, Qavion2 said:

In real life, you would most likely use this if one of your fuel tank quantity indication systems had failed.There is an MEL which applies. It has some rather critical procedures for making sure the tank has been fuelled to the correct quantity before flight (There are "dipsticks" in the tanks for checking fuel quantity manually)

Cheers

There are dipsticks! Very reliable and old school method. Works on boats and at your local service station too.