This is simple math. It is based on the parallax method. This method is the most accurate after the laser rangefinder, but has a longer range than the laser range finder. It can be used in different areas: on the golf course, in architecture, design, in geodesy, measure land or distance from wall to wall of your house. The range is from 1 meter (yard) to 10 km (miles) or more.
It is necessary to calibrate once in the normal mode and in the ZOOM mode.
After calibration, it measures a sufficiently accurate distance to the object, if the height or width of the object is known, within the limits of the camera's view of your device.