I'm with Jabawocky.
Recently installed a JPI EMS system.
When we did an actual fuel check ie drain the tanks the reading was within 5 litres after 150 hours of use with 24,000 litres going thru the tanks.
Beside which what idiot wants to fly round with minimum fuel nudging the 45 minute reserve. ( comment excludes those flying ex military types which have very different capacities)