Fuel gages are not know to be accurate. If your tank is round or any shape other than square box the gage is even more inaccurate. The gage only measure the height of fuel from top to bottom. To be off by 40 liters or apx 10 gallons is within the margin of error. That is my experience from putting fuel in a semi all these years. Heck I had one truck I could drive 300 miles before the needle even came off full. I had twin 120 gal tanks and the mechanic calibrated as he would twin 100 gal. tanks which was the company norm. I had to burn 40+ gallons before the gage would even start to move.
I'm sure if you look you will find a "weights and measure" sticker certifying the pump.
Safe travels
