I've been using this particular meter for about 4 years now. A durable meter; it's been dropped a few times. I almost always store the probe in the nutrient solution. I picked it up new around $100 when I was looking for a quality meter on a budget. This meter rarely if at all needs calibration... I usually calibrate before a new grow, and just double check with my drops occasionally throughout. I like the design better than pens; it's easier to read when sticking it in your reservoir. I recommend this pH meter to anyone looking for a mid-priced quality meter.