The distance seems to jump around from number to number. Why is this?

In this case the Nexus Rangefinder may be set to Scanning mode and not Target Lock mode. When Scanning mode is on the distance measurement will change automatically based on what the crosshair is focused on. Target Lock mode will ensure you only get the distance reading to one object. To switch from Target Lock to Scanning press the mode button 1 time. When Target Lock is active you will see a flag displayed in the left side of the display. When Scanning is active you will see no flag in the left side of the display.