I use a Milwaukee pH-56 meter and use (2) point calibration (7 and 4), at the start of each brew day. I've noticed lately that on the second point I initially get a "Wrong" reading, but then it will calibrate. I'm wondering if maybe an issue with the meter, or my process or the calibration fluids? The meter itself has not always displayed this characteristic. It seems to have started over the last 3-4 months. The issue has continued to show up after I have opened a new bottle of calibration solution.
I rinse meter in plain tap water and gently blow off, then first reading. After it registers I again rinse in tap water and blow off, then into second solution. The meter is about 3 years old, and the tip itself was replaced just over one year ago. It is cleaned using cleaning solution after each brew day and stored in storage solution until the next brew day.