Same one I own. Works great but yes get calibrating solution to remove any doubts re accuracy.http://www.amazon.com/HM-Digital-Thermometer-Measurement-Resolution/dp/B0002T6L5M View attachment 3314513You need the buffer solution to calibrate it http://www.amazon.com/General-Hydroponics-GH1571-1500PPM-REFERENCE/dp/B002YPLTCW/ref=sr_1_2?s=hi&ie=UTF8&qid=1418797067&sr=1-2&keywords=TDS calibration solution 1500 ppm