Its the leather flying helmet, coat and gauntlets that really make the difference Peter
Seriously though, I know nothing about GPS, but I thought it was for location and in case of need for diversion...not to tell the pilot what their fuel state is?? Don't get me wrong, I have nothing against a GPS, and I daresay i'll treat myself to one when qualified. Also the aircraft fuel gauge is good; and of course we all do our FEEL cx.... But fuel gauges and GPs systems can go wrong. It is then that you require a manual back up.