bluelab OnePen User Manual page 15

Wick contaminated or blocked.
Glassware aged or damaged.
pH calibrated with contaminated calibration
solutions.
Noisy – readings
Contact zone not immersed correctly.
jumping around
Scrolling text:
Incorrect probe has been connected.
"PROBE INVALID
FAKE OFF"
Pen won't turn on
Batteries are flat.
Probe not fully inserted.
Soak probe in KCl storage solution for 24 hours
and retest. Don't measure proteins or oils with
the OnePen™. You may need to replace the
probe.
Replace probe.
Re-calibrate in fresh calibration solutions.
Lower pen into solution at least 3cm/1".
Only use official Bluelab OnePen™ Replacement
Probes.
Replace batteries.
Make sure the probe is fully inserted, and that
the collar is tightened all the way.