The left trimpot (200kΩ) is the sensitivity adjust. The top resistor (10MΩ) is the hysteresis setup (~3KΩ tolerance) to avoid flapping when close to the switch limit. The right trimpot (120kΩ) and the switch are not components, they represent two poles inserted into the soil; in short, resistance is affected by soil moisture, drying it rises the resistance.
