The Martian calendar uses local years and days. The calendar began with the landing of the First Hundred, on Ls = 7 degrees of M-year 1, corresponding to circa September 2027.
Revolution around the Sun is divided into 360 degrees (Ls). The Northern hemisphere equinox between winter and spring was chosen as the Ls = 0 degrees.
A Martian year is 669 Martian days long and 687 Terran days long. It is broken down into 24 months; 21 months at 28 days and 3 months (every eighth) at 27 days. Month names are the same as on Terra, preceded by "1" or "2" to indicate to which set of 12 months they belong. For example: Friday, Ls = 101, 2 July 2, M-52, which corresponded to Terran day October 12, 2127 (the beginning of the Second Martian Revolution).
A Martian days lasts for 24:39:40. The 39:40 difference with the Terran day are called the timeslip, during which the Martian clock stops at 12:00 am.