Method and apparatus for preventing ambiguity in displaying the number

Abstract

A method and apparatus for indicating the number of the particular message that has been reached on a bi-directionally movable record medium used with a record/playback device. A position count is incremented and decremented as the record medium moves in forward and reverse directions, respectively; and end-of-message counts representing the locations of the ends of messages relative to an arbitrary reference location of the record medium are stored. Information representing the number of each message whose end-of-message count is stored is provided; and the number of the message which has been reached is determined as a function of which stored end-of-message count is greater than the present position count and which stored end-of-message count is less than that position count. To prevent ambiguities in determining the number of the message which has been reached, as when a new, partially used record medium is loaded into the record/playback device and is reversed to a location which precedes the reference location (i. e. the starting point of the record medium when it is loaded into the device), the position count is preset to a predetermined count when the record medium is replaced. This predetermined count is sufficient to prevent decrementing of the position count below zero, which would be interpreted as being greater than any of the stored end-of-message counts, even if the full amount of the newly-loaded record medium moves in the reverse direction.