Billrector,
I had a Safedip electronic tester that had to be calibrated monthly to a standard solution for PH according to the instructions. Not only that but the sensor had to be kept moist at all times. The sensor had a rubber boot with a small sponge in it. What a PITA! I believe all PH testers must be calibrated this way although I could be wrong. After using it for three months I sold it on ebay. I paid $140 for it and got $12 for it at auction. Lesson learned.
I had a Safedip electronic tester that had to be calibrated monthly to a standard solution for PH according to the instructions. Not only that but the sensor had to be kept moist at all times. The sensor had a rubber boot with a small sponge in it. What a PITA! I believe all PH testers must be calibrated this way although I could be wrong. After using it for three months I sold it on ebay. I paid $140 for it and got $12 for it at auction. Lesson learned.