The Hanna Instruments HI 721 Checker HC Handheld Photometer is a portable tester for monitoring iron levels . The HI 721 bridges the gap between less accurate chemical test kits, and expensive professional test instrumentation. The HI 721 operates using a silicon photocell light detector, and has an accuracy of + or - 0.04 ppm or + or - 2% of reading at 25 degrees C, using an adaptation of Standard Method 3500-Fe B. To use, zero the instrument with your water sample, then add the reagent. Place the vial into the checker, press the button, and read the results within seconds. The reaction between the reagent and iron within the water causes an orange tint in the sample. The HI 721 operates in temperatures from 0 to 50 degrees C (32 to 122 degrees F)/RH max 95% non-condensing with a range of 0.00 to 5.00 ppm (mg/L). The device operates on one 1.5 V AAA battery, with an auto-off function that shuts off the device after three minutes of non-use. Dimensions are 81.5 x 61 x 37.5 mm (3.2 x 2.4 x 1.5") and weight is 64 g (2.25 oz.). Colorimeters are used to determine the concentration of a substance in a solution by measuring the amount of light transmitted through the sample, often after adding a reagent. Iron colorimeters are used in water and soil analysis to monitor iron in ground water and industrial, agricultural, and mining run-off. Hanna Instruments manufactures a wide variety of analytical instrumentation, including pH meters, multi-parameter meters, electrodes, chemical reagents and buffer solutions. Founded in 1978, Hanna is headquartered in Woonsocket, RI, with subsidiaries in 32 countries. Hanna Instruments holds many firsts in the field of analytical instrumentation, including a pH electrode with a built-in temperature sensor, an electronic pocket-sized pH tester, and a replaceable electrode pH pocket tester. To ensure the quality of their products, Hanna is a vertically integrated manufacturer and does not subcontract any part of its manufacturing. Whats in the Box? Two sample cuvettes and caps Six powder reagents One 1.5V AAA battery Instructions