Three primary variants of the tricorder appear in Star Trek, issued by the fictional organization Starfleet. The standard tricorder is a general-purpose device used primarily to scout unfamiliar areas, make detailed examination of living things, and record and review technical data. The medical tricorder is used by doctors to help diagnose diseases and collect bodily information about a patient; the key difference between this and a standard tricorder is a detachable hand-held high-resolution scanner stored in a compartment of the tricorder when not in use. The engineering tricorder is fine-tuned for starship engineering purposes. There are also many other lesser-used varieties of special-use tricorders. The word “tricorder” is an abbreviation of the device’s full name, the “TRI-function reCORDER”, referring to the device’s primary functions; Sensing, Computing and Recording.
Source: Wikipedia
