Martel Electronics 320 - Manual (Page 12)

The LPS battery voltage should be between 10.6 and
9.2 volts, indicating a full charge. When the voltage
falls below 8.8 volts, the LPS will turn itself off to
prevent damage to the batteries due to possible cell
reversal.
SELECT KEY
The Select Key is used for two functions. First, while
in Setup, pressing Select will switch the dispay from
two sets of menu screens. Second, Select is used in
the field calibration described on page 26.
ZERO KEY
When the Model 320 is first turned on, a small zero
offset may appear. Pressing the zero key wil eliminate
it. A warm up of up to four minutes may be required
to achieve nominal accuracy. For absolute pressure
sensors only, the following procedure may be used.
Press the Zero Key. The calibrator will request the
user to enter the calibration access code (found on the
factory calibration data sheet.) After entering the code
and pressing the enter key, the calibrator will prompt
the user to enter the new zero (actual barometric
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