The confusion comes from the fact that a metered gallon isn’t a gallon most of the time…
with home heating propane it isn’t a problem because all of the delivery truck meters are required to be adapted to compensate for temperature…
most sellers readily agree to this added expense because without it in cold weather when they sell the most propane they would be short changing themselves…
As far as I know small cylinder propane filling stations are not required to have the ATCD, most likely because each sale is such a small quantity…
But a pound is always a pound…