Which of the following is NOT a direct cause of instability in a receiver?

Instability in a receiver refers to its inability to maintain a constant tuned frequency, commonly experienced as frequency drift. This is typically a physical or electrical issue caused by changes in temperature, poor mechanical rigidity (which allows vibrations to alter the values of capacitors or inductors), or faulty feedback components within the oscillator circuit. Dial display accuracy, on the other hand, simply describes how well the radio's display matches the actual tuned frequency. A poorly calibrated dial might cause the operator to misread the frequency, but it is a passive indicator and has absolutely no effect on the electrical or mechanical stability of the receiver itself.