Product review (5 stars): Calibrating this thing will be the death of me. Revised. Seller really went the extra mile to make me happy, and did NOT ask me
This is a nightmare to calibrate, and it won't stay calibrated.  Also, I have calibration solution at 7.00.  However, this only calibrates at 6.86 and 4.01, so you need to continually buy the powder.  I love the idea of it.  But for now I still need to use my 9 dollar one that calibrates with a screwdriver instead of electronically.  If I get my question answered about how to keep it calibrated for longer than 30 seconds and it works I can change this, but for now just one star.  Update.  The seller did not give up.  I returned it, got a refund. They sent a new one anyway and explained the other one really was not working, then helped me with the calibration of this one.  At no point did they ask me to change my review. This seller has integrity,