The REOTEMP Moisture Meter measures the moisture content of your soil or compost pile by means of a sensor at the bottom of the probe. While composting or gardening you often may wonder: How wet’s your soil? Now you will know and be able to more efficiently compost, garden or simply know if your plants need more water. The 0 to 10 scale of the MM15 indicates a relative “wetter” or “dryer”. Note: the probe does not display a percent moisture. The moisture meter measures moisture only at the tip of the probe. Calibration instructions are conveniently printed on the side of the meter head and included on the back of the box. The REOTEMP moisture meter uses 1 AAA battery. Please note that because the probe uses electrical conductivity, the presence of salt can affect readings by making your soil more or less conductive. Therefore, the REOTEMP moisture meter is not recommended for situations where salt content varies drastically between testing samples.