Never had to think about this until yesterday when a friend who is a gas licenced mechanic ( new and learning from me ) had a customer with a fuel gauge readout problem.
After much testing we decided it was the float unit bubble was leaking liquid in under pressure and sinking to the bottom giving an empty reading. Of course , on removal at atmospheric pressure there was no liquid in the float to indicate problem on removal. Replacement fixed the problem
On a side note, the customer was told to bring the car back when he had used all the gas. He asked to borrow a screwdriver until he returned. Suspiciously cautious we decanted the gas instead at that time. The owner later admitted that he intended to release the gas and investigate the internal sender problem himself by undoing the four sender retaining screws. When he saw how we and what we did he admitted he coulda killed himself had he been able to borrow the screwdriver, as the sender removal exposes the tank contants under pressure !!