M03c refers to M03 messages that began and ended with the groups "77777 77777", which were included in the amount of groups given in the preamble. First heard in August 2000, last heard on 4 December 2008.
Format is given below. The speed was always 15 words per minute.
|233||/||36||BT BT||77777 77777 77777 77777 90432 90432 ... 15369 15369 77777 77777 77777 77777||BT BT||233||/||36||BT BT||77777 77777 90432 ... 15369 77777 77777||BT BT 0 0 0|
|3-figure ID||Amount of 5-figure groups in the message, including 77777's||5-figure paired groups||3-figure ID||Amount of 5-figure groups in the message, including 77777's||5-figure single groups|
|Repeated for 3 minutes and 20 seconds|
On each schedule, an M03c message would have been sent on one random week of each month. The messages were never shorter than 30 groups, and never longer than 39. M03 messages sent from mid-2008 onwards also have the same group count constraint, but no longer contain "77777" groups - however similar groups are still present in its digital counterpart, POL FSK.