It should be easy to irrigate accurately. Soil holds water like a sponge. Each day the plants extract some of this water via their roots and transpire it through their leaves. Some water also evaporates from the soil surface.
Accurate irrigation is simply replacing what has been lost. However, it's not always so easy in practice.
The FullStop Wetting Front Detector helps you to "see" what is happening down in the root zone when you irrigate the soil. FullStops are buried in the root zone and pop up an indicator to show when the infiltrating water goes past. FullStop has no wires or batteries.
The FullStop also collects a water sample from each wetting front so you can track fertilizer and salt movement.
This site guides you through some of the mysteries of what happens down in the soil when we apply water at the top.