IVR is the instrument voltage regulator. It is a bi-metalic thermal switch that regulates that average voltage based on on-off duty cycle. The gauge operation is thermal, the meter movements are driven by thermal expansion. The IVR pulses, but due slow thermal nature, bounce is not typically a problem, if the switching frequency is high enough. IVR can wear over time, and fail, but I would think the rest of the gauges would bounce too, fed from same regulator.
