This is a resistor that can be installed in line in your temp wire. It can be set to your engine temperature for gauge accuracy.
The number of degrees of engine temperature change on the dash gauge varies greatly with the values of the dashgauge and engine mounted sending unit used. This is the reason we need this device so often. There were so many variables in these values sold over the years that the temperature readings on the dash are all over the board.
The variable resistor kit should correct almost any gauge that reads higher than the actual engine temperature. It has a resistance range of 50 ohms. That is, it sweeps from zero ohms to fifty ohms with 17 turns of the screw. This large number of turns on the screw enables you to adjust the needle on the dash gauge very accurately.