I dont blame MD on this as it is more of a curiosity question for the time being. I purchased a Pinpoint Calcium monitor a month ago when MD first introduced it. So far it appears to be a piece of ----p. Reading vary wildly. I've calibrated it several different times and it keeps drifting after a day or two. I have it setup for constant monitoring and according to instructions and is not set deep enought for water to enter the fill hole. I accepted the reading as accurate and I poisoned my tank by overdosing calcium chloride when it showed a low reading for several days so I am not a happy person. Reading were showing 275 when according to traditional test kits(2) it was acctually over 500. Then the monitor after recalibration and a couple of days and several water changes again showed to be over 750. Test kits showed 450. It appears to be fairly accurate for two to three days then goes stupid, instructions say should only have to be calibrated every few weeks. I see no signs of cracks or leaks. I keep the membrane clean. This is a fairly new product an am wondering if you are getting complaints from other users.