At the attached photo you may see a type of pocket pH meter.
On the following link you can see the pH meter dismantled:
The manual says:when you finish the measurment,you need to clean/stir the electrode bulb with distilled water,
DRY the electrode bulb and replace the protective cap before store the ph meter.
As far as i know,ph bulb electrode should be stored wet or be in a storage solution.
Could it be that this type of ph meter has a different technology/operation?