Only an approximation of the existing fuel level may be provided by the float tank gauge with LTD-level temperature and density. It may even fail to provide a good estimate if the float mechanism has malfunctioned.
Removing the outer shell and pushing the float downward is one method to check. The float should rise on its own after you release it. If it does not, you have a faulty float that requires expert repair. This can occur as a result of normal wear and tear on older tanks.
Also, the arm beneath the tank gauge with LTD-level temperature and density might swivel and become jammed against the side of the tank. Finally, floats might become coated in thick muck, which weights them down and prevents them from functioning correctly.