6 in 1 TDS Meter, TOC Meter, Meter, UV275 Meter, Electric Conductivity Meter & Temperature Meter Water Testing Kit features the most updated technology with high precision. Wide test range makes it fits multiple uses, tap water, well water, water purified by drinking fountains, bottled water, ground water, water (not sewage) and other drinking water & TOC refers to organic pollution and other hazardous substances. These types of tests can usually only be done in laboratories, but our high end water testing pens can perform these functions. Normally TDS can only detect minerals and other dissolved solids in the water, and the TDS value alone cannot be used as a criterion for judging the quality of the water. The probe is a laboratory spectroscopy probe, the device power on prompts "calibrate within a week", in order to facilitate laboratory use scenarios. For less rigorous daily home use or outdoor travel use, weekly calibration is not required. If you accidentally measure into sewage,