Laser range meters provide an alternative or supplement to standard tape measures for obtaining measurements at scenes. Such measurements taken at scenes are typically for documentation purposes. It is necessary to have accuracy sufficient to produce a fair representation of the aspects being documented. Team Leaders assess diagrams prior to their distribution to ensure they are a true and “accurate” representation of the scene.
Laser range meters emit a visible laser beam with measuring waves. During use, the beam is reflected off a target surface and bounces back to the meter, returning to the unit with a phase shift to the measuring waves. This phase shift is measured by the range meter and used to accurately determine the distance between the unit and the target surface. This does not typically require special reflectors on the target surfaces.
The unit utilized by the crime scene team is powered by two AA alkaline batteries, which will provide 15,000 to 20,000 measurements (battery life shorter if display illuminated). The measuring range of the unit is 2 inches to 600 feet with a typical accuracy of + 1/16 inch. Operating temperatures range from 140F to 1220F and the unit can be stored at temperatures of -220F to 1580F. The unit is most often used for measuring indoor scenes. For outdoor scenes an electronic distance measuring device (EDM) similar to that used by surveyors is more often used.
Below is a diagram of a scene typical of what can be produced through measurement taken with laser measuring devices or tape measures.