 Most reed relays in the crossbar switching systems of the 1940s through the 1970s were packaged in groups of five.Such a "reed pack" was able to store one decimal digit, encoded in a two-out-of-five code (74210 code variant) for easy validity checking by wire spring relay logic.Such an electrically latching reed relay requires continuous power to maintain state, unlike magnetically latching relays, such as ferreed (ferrite and reed relay) or the later remreed (remanent reed relay).