TESTO 523 Instruction Manual page 13

Close battery compartment.
3
Set battery type and check/set date/time, see chapter First s s teps,
4
handling objective Switching i i nstrument o o n.
Replacing t t he v v alve o o r t t he p p ositioner k k nob:
Warning!
Replacing of the positioner knob and the valve by the customer is not
allowed. Send the instrument to Testo customer service.
Maintaining the product 13