You have assumed that when I said "when the main tank is empty", I meant empty on the gauges
How could I possibly assume that? You were quite clear in that you were saying that when the actual main tank is empty, the gauges will still indicate a quantity.
More seriously though, what you are suggesting Drinkgirls is that the tests that were completed on the manufacturers EC135 Articulated Fuel System Test Rig, from page 54 in the report, were incorrect.
"The supply tank actually holds more than 90kg, it is DISPLAYED as 47/43 (ish) and a bit is added to the main contents as well.
Really, it IS fact"
page 59;
One test point replicated the orbit at Dalkeith, as much as possible. The orbit was flown at 30 kt, with an indicated nose-up attitude of 5-7°, in level flight. The fuel on board at the start of this test consisted of 47 kg and 43 kg in the left and right supply tank cells respectively, with 97 kg in the main tank. After four minutes, the indicated fuel in the left and right supply tank cells remained the same and the amount in the main tank had reduced to 82 kg.
(Main tank started with 97 kgs, 4 minutes later had 82, consistent with a 3.5 kg/min burn rate.)