A low power beam is sent out from a laser rangefinder and its return time is measured. The distance to the object that reflects it is calculated from this elapsed time.
Some laser instruments tell the golfer the elevation change to the target. This is done with an internal inclinometer that measures how far from level it is when a reflection is received.
GPS devices determine their position from received satellite signals and then calculate distances to course features. The satellite signals are digitally encoded to identify the exact times they are sent, and the elapsed time from each satellite pinpoints the device's exact position.
GPS Rangefinder Apps
With advances in smartphone technology, there are now numerous GPS rangefinder apps available for purchase. These apps use the same technology as traditional GPS rangefinders but without having to putchase additional hardware, instead using your phone's built-in GPS system.
The exact positions of the satellites are stored in the GPS device by the manufacturer, and a database with known objects on the golf course must be loaded before using it.
On-Cart GPS Systems
Many golf courses have GPS systems built into their carts. The daily updates they receive at the course allow measurement to the pin positions as well as to major objects.