lpg gauges are pooh....but can be improved...if a standard 0-90r then a vdo fuel gauge could be used..or get the software for your system and set the gauge up as non standard..that way you can set the 3/4 1/2 etc to be accurate..
(i get over 300= for 90l..(average driving)up to 400 if really careful..or less than 100 if booting it..4l s/c.megasquirt ecu. )