A refractometer is an optical instrument that is used to determine the refractive index of a substance or some physical property of a substance that is directly related to its refractive index. Most commonly, refractometers are used for measuring fluid concentrations such as the sugar content of fruits, vegetables, juices and carbonated beverages. Kernco Instruments claims its 300051 operates at within a range of 0-65 per cent, which the company claims is an industy lead against competing products with ranges of 0-35 and 0-45. Concentrations can be accuratelty measured of liquids at temperatures up to 40C (104F) and readings are displayed on the screen within one second, the manufacturer claims The waterproof unit is housed in stainless steel and requires a single AAA alkaline battery. To save battery power, the unit shuts off automatically if unused for three minutes. Up to 8,000 readings can be taken using the power from a single battery, Kernco claims. Each unit is supplied with a carrying case, battery, pipette, instruction manual and standard a five year warranty.