During a survey, the depth of the probe is controlled by aligning depth marks on the control cable to a reference, such as the top of the casing or the top of a pulley assembly. If you want depths on the plot to represent depths below ground surface, then you should enter an offset to adjust the reference to ground surface. That is the purpose of the offset field.
For Depth Offset, enter height of casing above ground level + height of pulley (1 ft or 0.3m)
Metric Example: Suppose the top of the casing is 0.5 meters above ground level. You use a pulley and index the cable to the top of the pulley (add 0.3m). Enter 0.8 m as the depth offset. Labels will show depth below ground surface. .
English Example: The top of the casing is 14 inches (1.17 ft.) above ground level. The pulley assembly adds 1 foot. Enter 2.17 feet for the depth offset. Labels will show depth below ground surface. .
For Elevation Offset, enter ground elevation + casing height + pulley height
Metric Example: Ground elevation is 200 meters above sea level. The top of the casing is 0.4 meters above ground level. The pulley assembly adds 0.3 meters. Enter 200.7 meters for the elevation offset. Labels will be referenced to ground elevation.
English Example: Ground elevation is 1200 feet above sea level.
The top of the casing is 1.5 feet above ground level. The pulley assembly adds 1 foot. Enter 1202.5 feet for the elevation offset. Labels will be referenced to ground elevation.