ACCURATELY TEST YOUR SOIL ANYWHERE IN ONLY 3 MINUTES !! The Kelway professional direct pH soil tester is used by thousands of nurseries across the world. It operates on the principle of electrical potential between two dissimilar metal plates. (Extremely Accurate to +/- .2) Very durable. No batteries required. When inserted into moist soil, the HB-2 registers degree of acidity on the upper scale. The lower scale shows the degree of moisture (% saturation) when the button is held depressed. Comes with a handy carrying case with belt loop and complete instructions including a guide for changing soil pH. Why choose a Kelway Professional soil tester? Litmus paper is difficult to use and interpret. Laboratory glass elctrode pH meters require buffer solutions, temperature control, power sources, clean equipment and they are both fragile and expensive. Soil brought to the laboratory for testing often changes pH enroute before it can be tested due to CO2 losses and you must wait for the results. The Kelway Professional pH tester is portable, rugged, convenient, operates without a power source and is not overly sensitive to temperature variances. This instrument is 6 1/2 inches long and weighs 8oz. Great for individual pots or for entire beds. Customers note: Highly alkaline soils can cause erroneous readings with this meter.