Review on Accuracy Measurement Household Drinking Aquarium Kitchen & Dining by Erin Jackson

It's easy to use and comes with instructions for the calibration powder. RINSE WITH DISTILLED FIRST REQUIRED according to directions. I just wanted to get that across because if you're like me, you don't have this home. It speaks of recalibration when a lot is used for accurate measurements. I would say it needs to be recalibrated right out of the box as refills are 0.002 gauge right out of the box. The actual reading may take 1 minute before the number levels off. Sometimes it measures quickly, sometimes it's better to leave it in solution for a while. Overall, it's good for tracking your pH and testing water systems.