Did you know that Smith's gauges operate on 10 volts DC? The reason for this is that the gauge has to be accurate no matter what the condition of the battery and charging system. So while your car operates at 12-14 Volts DC, a small voltage regulator in your dash reduces voltage to the required 10 Volts. This voltage regulator drives the fuel gauge and temperature gauge. (Your oil gauge has a regulator built into the sender, while the voltmeter or ammeter operates at system voltage.)
The stock IVR is an antiquated electromechanical device, but CoolCat's solid state Instrument Voltage Regulator replaces it perfectly. It regulates voltage using modern solid state circuitry, so your gauges will be more accurate. The circuit is protected against smoke releasing surges.
But that's not all. The voltage of CoolCat IVR's can be adjusted with the turn of a dial. This allows you to adjust the calibration of your tired old instruments, without having to incur big repair costs. (Two solid state IVR's would allow you to calibrate each gauge independently.)