There are various types of temperature gauges, those with expanding gas sensor, those with a thermo-couple sensor, & those with a transistor temperature sensor. In my opinion, the least accurate and least reliable type temperature gauge is gas type.
> The gas temperature sensor uses ether to expand a coiled tube in the gauge. The coiled tube is known as a Bourdon Tube. The failure mode is leakage of the gas. This type of gauge is era correct for the Model A.
> The thermo-couple sensor has 2 different metal wires welded together in the sensor. As the temperature increases, the differential metals produce a voltage that is indicated by a gauge with a D'Arsonval electromagnetic movement. This type of gauge is also Model A era correct.
> The digital gauge uses a transistor as a temperature sensor. As the temperature of the transistor changes, the current output of the transistor changes & is displayed with a gauge containing a digital ammeter. This type of gauge is correct for post 1950 vehicles, but usable in a Model A.
The Rex-A-Co Gauge is a gas type & the APCO Gauge is a thermo-couple type.