Irrometer sensors come made for soil (outside, gardens and farms) and for planting and potting mixes (indoor, greenhouses, and outside beds). This one - best for using with potting mixes - includes four sensors and the parts needed to set it up: a hand vacuum pump, a bottle of Irrometer fluid, 25 monthly chart forms, and a reference book. After setting up the sensors, you can use the pump to remove air from them to ensure maximum sensitivity and accuracy.