Calcium presence in water supplies results from passage over deposits of limestone, dolomite, gypsum and gypsiferous shale. Its concentration may extend from 0 to several hundred milligrams per liter, depending on its source and treatment. Calcium is necessary in plant and animal nutrition since it is an essential constituent of bones, shells and plant structures. Calcium in water as carbonate is one of the primary components of water hardness which can cause pipe or tube scaling. The HI 758 Calcium Checker HC is extremely simple to use. First, zero the instrument by adding Reagent A, deionized water and 0.1 mL of sample into the vial. Insert into the HI 758 and press the button. Next, remove the vial and add Reagent B and shake to dissolve. Reinsert into the Checker HC and press the button to read the calcium concentration in ppm on the display. Use for quick and accurate on the spot analysis. Single button operation: zero and measure. Range: 200 to 600 ppm. Resolution: 1 ppm. Accuracy at 25 degree C: +/-6% of reading. Light Source: light emitting diode at 610 nm. Light Detector: Silicon Photocell. Environment: 0 to 50 degree C (32 to 122 degree F); max 95% RH non-condensing. Battery Type: (1) 1.5V AAA. Auto-off: after 10 minutes of non-use. Dimensions: 81.5mm x 61mm x 37.5mm (3.2" x 2.4" x 1.5"). Method: adaptation of the zincon method.