Measuring the backsight target height

There is a height measurement mark on the side of the prism base that can be turned out for easier reading of the height. The height measurement mark is 0.158 m (0.518 ft.) below the target (signal) height. Measure to the top ridge of the mark.

When there is a controller attached running field application software such as Trimble Field Software, the software has additional functions that reduce the bottom mark measurement to the required vertical target (signal) height.

The measured distance (Hm) is corrected for the slope of the measurement to obtain a vertical measurement to the bottom mark (Hc). The constant from the target height measurement mark to the target (signal) height (0.158 m/0.518 ft.) is added to the Hc to obtain the vertical target height from the ground mark to the target (signal) height (Th). For more information, refer to the field software documentation.

Alternatively, to obtain an accurate measurement to the target (signal) height (Th), you can manually measure the slope distance from the ground to the bottom mark (Hm). To calculate the total target height (Th), insert the measured slope distance (Hm) into the formula below:

Th = 0.158 + √(Hm² – 0.091²)