B&K Precision 307A - Manual - Manual (Page 11)

10.2 DC Warning
The DC warning buzzer will beep continuously when
DC voltage is higher than 30Vdc on the test probes
and the test button is Not pressed.
The neon light "circuit live" will lit when the voltage
on the test probes is higher than 90Vdc and the test
button is not pressed.
10.3 AC Warning
The AC warning buzzer will beep continuously when
AC voltage is higher than 20Vac on the test probes
and the test button is Not pressed.
The neon light "circuit live" will lit when the voltage
on the test probes is higher than 65Vdc and the test
button is not pressed.
10.4 AC Measurement
The AC measurement is automatic on this instrument.
as soon as AC voltage is present on the test leads,
the instrument will display the AC voltage from 20 to
600Vac on the linear scale.
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