The porous ceramic tip is used to measure the moisture as water is sucked out of this tip if the soil is dry. This results in negative pressure in the plastic tube which is shown on the display. The drier the soil, the higher this negative pressure reading. After watering, the water is sucked back, the plastic tube fills with water again and the negative pressure reduces.
The simplest way of measuring moisture. The best way to find out how much water your plants need is to leave the Blumat Digital in one place.
If you move it, give it 2 to 3 hours to show an accurate measurement.