Warm-up time.
The warm-up time for the main instrument without preamplifier/microphone is very short and the instrument obtains
the final accuracy as soon as the self-test is made. Used with a preamplifier and microphone, this time can be
prolonged due to the charging of the microphone with the polarisation voltage. Normal sensitivity is reached within
one minute. Before a recalibration is attempted, at least two minutes for warm-up is recommended.