The marks on the sensor shaft indicate the depth of the sensor in the ground. It can be used as a reference in order to find the right depth for your soil sensor setup. 

To place the sensor at the desired depth, keep an eye on the marks you can see on the sensor (see figure 6). If you know the required depth and want to calculate the number of marks that must be visible for the respective depths, see figure below.

The calculated depth is measured from the center of the watermark sensor to each mark on the shaft of the housing.

Example: If you intend to place the middle of the watermark sensor at 14 cm deth/5.5 inch you need to make sure that the top mark is at soil level (0 visible marks above soil level). If your intention is to place the middle of the sensor at 6.5cm depth (minimal depth) the first mark should be at soil level and 5 additional marks should be visible.