Laser rangefinders are devices that contain a laser and can be used to measure the distance between two points. A gadget like this usually uses either the direct time-of-flight method or the phase shift method. At the US Army’s Pitman-Dunn Laboratory in Frankfort Arsenal, Pennsylvania, the first artillery laser rangefinder was created using ruby. This gadget, dubbed the XM23, was the first of a broader family of rangefinders. Until the introduction of the M1 Abrams tank series in 1978, the well-engineered ruby laser rangefinder was installed in every main combat tank the US Army fielded. Although the ruby laser system was important in early research, the introduction of Nd:YAG as a lasant later allowed for quicker and cooler lasers to be integrated on the M1 Abrams and the conversion to M1A1 Abrams.