Food for thought: My old guage functioned similar. My new one, instaleld in about '89 was/is better. The problem with the new one is that, although it will read below a quarter and still have gas, I ran out one time with a quarter showing on the guage.
I call it empty when it reaches a quarter. And it may as well be empty because if it reads accuratly, from a quarter reading to aucking air is only a few miles down the road.