Tds stand for TOTAL dissolved solids, which includes salt, metal or mineral in the water. A tds meter is an easy to use hand-held digital meter to instantly check your overall water quality. It allows you to stay on top of your drinking water quality at all times! with the push of a button, the tds meter can tell you your overall water purity level, which will be displayed on the screen measured in parts per million (ppm). the lower the number showing on the tds meter means the purer the water quality, with 0 ppm being perfect and pure water. The tds meter is a great tool for water filtration, water purification and drinking water. It is also great for checking your tap water quality, or knowing when to change your filters for your water filter systems. Replaceable 3V battery and vinyl case included specifications: range: 0-1999ppm tds sensitivity: 1 ppm tds probe material: stainless steel storage temperature: 0°c ~ 80°c operating temperature: 10°c ~ 40°c dimension: 128mm (L) x 25mm (W) x 20mm (h) weight: 1.24 oz. Battery type: 3V CR2032 factory calibrated: calibrate with a 300 ppm 442 solution apec water does not distribute or sell our products to any 3RD party sellers on Amazon. Please purchase genuine apec water products from Amazon or apec water directly for authenticity.