Thermo Fisher Scientific Alpha pH 190 (In the process of updating the brand guideline & product image) - Manual (Page 20)

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If you are performing a 1-point calibration, press the ▲ and ▼keys
together to return to measurement mode. If you are performing a
two-point calibration, proceed with the next step.
1. Use
▲ or ▼keys to select the next buffer value (pH 1.68, 4.01,
9.18, 10.01 and 12.45).
2. Make sure the electrode is in the correct buffer solution. Allow
the electrode time to stabilize.
3. Press ENTER. The instrument blinks with the un-calibrated pH
value corresponding to the mV output of your pH probe. If the
value displayed differs substantially from the buffer value, this
indicates electrode drift. Consider replacing your electrode.
4. Press ENTER to confirm the buffer value. The display blinks
the calibrated value twice and flashes “DONE”. Press ENTER
again to return to measurement mode.
NOTE: Buffer must be within ±1.0 pH of the value you are
calibrating to, or Err1 will display. To clear the Err1 display and
return to calibration mode, press the ▲ and ▼keys together.
NOTE: You can view the pH calibration points in the Setup
program. See Section 9.6 for details.
The slope and offset are re-determined after each calibration.