Per Stewart Warner specs, these are 80-10 instruments. 80 ohms = no needle movement. In the case of fuel gauge, 73 ohms will lift the needle to the first/empty hash mark. The tester used by service techs had less than 80 ohms for starting point because 80 or greater ohms would not have been a test. 80 or greater leaves you scratching your head, "Does it work or not?" I hope that makes sense.The full tank resistance is closer to 74 Ohms. So 80 isn't awful.
Maybe it also matches the later fuel gages @RedFish mentions in this post: Gauge Cluster Issues/IVR
@toolmanmike This shows the internals and more
Thermal-Electric Gauges (Session 227) from the Master Technician's Service Conference
Half range is 23 ohms. Calculator says half way between 80 and 10 is 45 but that's not how a thermal resistor instrument works. As a thermal resistor wire heats up its per inch resistance changes. Max range is 10 ohms.