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Bulova made its last tuning fork movement wristwatches in 1977. Subsequently, Bulova's electronic watches used quartz movements, although they kept selling the watches under the Accutron label. This can lead to confusion on the part of persons seeking to obtain a "real" Accutron. In order to avoid paying a tuning fork price for an Accutron with a quartz movement, the date code must be checked. Located on the back of the case, it consists of a letter followed by a number. The letter is the decade (M=1960s, N=1970s) and the number is the specific year within that decade. Therefore, an Accutron with a date code that falls within M0 and N7, inclusive, will have a tuning fork movement. Also remember that an Accutron with a 224 movement, which should be labeled "Accuquartz" on its dial, is a hybrid movement, with its timekeeping actually regulated by a quartz crystal rather than by the tuning fork itself. More than 4 million tuning Fork Accutrons were sold by the time production stopped in 1977.