As one of your 'minimalists', Meikleour, what point are you trying to make? Here I give you yet another excuse to ignore the calculated PLOG fuel and bung on a bit more for Mum?
When I land, wherever that might be, I calculate, both in Kgs and in litres, the fuel I need to fill the tanks with the amount I require to accomplish the flight. When the two figures are compared they rarely differ by more than a few tens of litres.
The gauge normally reads within about 10-20kgs and has never read more than about 40-60kg different from what I am expecting, so once again, just what is your point?
The gauges are accurate.
If you need an excuse to ignore the PLOG, find something else to hang your hat on.