Incorporate the world's first flat sensors, these compact pH meters are able to take accurate pH value (acidity - alkalinity) measurements from a single drop sample. The unique flat sensor allow measurements of powder and solid object samples be easily taken. The Twin pH meters can be used to measure the pH value of a wide variety of items including tropical fish tank water, river water, drainage treatment solutions, hair, cloth, food, soil, and rainwater. Three models are available; the B-211, with one-point automatic calibration, and the B-212/B-213 model, with two-point automatic calibration.