DiST’ s are rugged and reliable pocket-sized testers that offer quick and accurate readings of conductivity or TDS. The DiST® family of testers is widely used for monitoring EC/ TDS in drinking water, water conditioning, reverse osmosis, cooling towers, wastewater, laboratories, agriculture, aquaculture and aquariums, hydroponics and the printing industry. This tester features an amperometric graphite electrode that provides better repeatability in measurements since they do not oxidize. An amperometric measurement of EC is based on Ohm’ s Law, I = V/ R where R depends on the distance between two pins and their surface. Oxidation changes both the distance and surface which will affect accuracy. The DiST’ s non-oxidizing graphite pins are able to provide an optimal surface for accurate, dependable results. When calibration is necessary, simply submerge the electrode tip into calibration solution and adjust the trimmer on the side of the tester. Order Information: HI 98304 ( DiST 4) is supplied with protective cap, screwdriver, batteries and instructions.