You can get some idea of gauge calibration accuracy by measuring the resistance of the sender at "known" intervals, IE full, 1/2 and empty
One easy way is to access the left kick panel, and separate the rear harness connector. Look up the wire color for the sender and measure that to ground "when" you have some idea of amount of fuel in the tank. There are many threads here on gauge testing. Here are the old gauge tester readings:
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