From the Manufacturer

The KS-D1 Digital Soil Moisture Tester, used with the GB-1 Gypsum Soil Blocks, make up a valuable system to monitor the soil moisture available to the plants. This system eliminates guesswork so that irrigation can be effectively scheduled according to plants' requirements. The KS-D1, housed in a rugged ABS plastic case, features reliable temperature stable semi-conductor technology with internal battery and calibration checks for users' full confidence. A membrane switch panel provides positive, tactile feel. Spring-loaded binding posts allow for positive contact with the blocks' leads.