What does the term drift mean in relation to pH measurement, and why should I be concerned about it

The subject of the above question is comprehensively covered in the technical paper entitled Care, Maintenance and Fault Diagnosis for pH Electrodes published by J. J. Barron, C. Ashton. & L. Geary of the Reagecon Technical Services team.

The technical paper includes details of practical remedial actions which can be taken to improve the accuracy of pH measurements and extend the working life of pH electrodes.