This tester measures soil acidity with use of 2 electrodes : one is made of special alloy that candevelop the same electromotive force as hydrogen potential, while the other is made of zinc.This tester has the function of, in combination of these 2 electrodes, developing the electromotiveforce by hydrogen ion in the soil, and then, moving the pointer. The following is explanation ofchange in case of actual usage example.First, if this tester runs with the special alloy electrode as positive pole having the same electromotiveforce as hydrogen potential, the pointer wil indicate less than pH 7. However, in case of more thanpH 7 ; alkalifying, the zinc electrode, elaborating “zinc amalgam”, will automatically change to the positive pole. Also, the special alloy electrode will run as negative pole and the will indicatecommensurate value to hydrogen ion concentration.