I agree strongly with djrockinsteve about the usefulness of pH meters but mine (a Hanna) can be a pig to calibrate. I may be wrong but I work with the assumption that even if it is out of spec each time I turn mine on, I am looking for a rough estimation and not precision to the third decimal place, so I calibrate mine infrequently or only if I am going to be testing a number of batches. If the reading I get is 3.5 and it should be 3.7 or 3.3, I am not going to worry. Or should I?