Improved precision
Analog frequency correction

The precision required generally leads to gain values that make the control system unstable if a simple proportional corrector is used. For the example in question, if an error of 1% is required, the corrector would have to have a gain of 20 dB (given the system's gain of 20 dB, because then 1 + A _c K = 1/ε ₀ = 100, i.e. A _c K " 100 = 40 dB, hence A _c = 20 dB); this would therefore be a gain greater than the oscillation gain A ₀ , so the servo would be unstable.

A low-pass corrector, or its proportional and integral version, increases the gain for the same closed-loop overvoltage while maintaining the same resonance pulsation.