A great all-rounder. It is designed to determine total hardness (as CaCO3) in drinking and process water, heating and cooling systems, swimming pools and spas. Also suitable to be used in agriculture, food and beverage industries. This handy Checker is easier to use and more accurate than chemical tests kits. It is dedicated to a single parameter. It has single button operation system and easy to use. The large LCD is easy to read and the auto shut-off feature assures the battery will not be drained. It may be small, but it is certainly a big convenience! Ideal for: Drinking water Process water Heating and cooling systems Swimming pools, hot tubs and spas Agriculture Food and Beverage industries Water Hardness Guide Hardness classification Parts per million (ppm) Grains per gallon (gpg)* Very soft <17.1 <1.0 Soft 17.1 to 60 1 to 3.5 Moderately hard 61 to 120 3.5 to 7.0 Hard 120 to 180 7.0 to 10.5 Very hard 180 + 10.5 + * 1 grain per gallon = 17.1 ppm