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The five-dar rule is thus somewhat simpler to implement, since it involves only addition. The four-dar rule is more complex in its implementation, since it involves detection of a value of 50, which is not a modulo 4 result, and involves both addition and subtraction operations. The five-dar rule runs consistently behind, and the four-dar rule causes the error to have both positive and negative values. This latter rule gives a slightly better average error. |
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At this point, it is possible to specify the logic for a Martian clock. The major point of difference from a Terran clock is the need to retain the dar count in a two-digit register and alter the reset logic to use the register. To simplify the process of resetting the correct time, some additional ROM logic would be useful to carry information relating cumulative error to dar number. |
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9.13.2.1.9
Year Types and Cycles |
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Martian yar types follow a regular succession, although the order of Martian yar types will be different from the Terran. The order is, in fact, simpler than the Gregorian or even the Julian. In the Martian calendar, there are at least three cycles of yar type: |
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1.) A minor cycle within a single mard. Leap and common yars alternate within a mard. Common yars end with an offset of (+3) dars from the DOW of their beginning. Leap yars end with an offset of (+4) dars from the DOW of their beginning. Thus, when a leap yar is followed by a common yar, the dar offset is the sum of (+4) + (+3), or seven dars. An offset of seven dars, however, returns the DOW to the one which started the pair, so the effect is no offset at all. Thus, within a single mard, all leap yars start on the same DOW and all common yars start on the same DOW. Any pair of yars that contains one leap yar and one common yar comprises (669 + 668 =) 1,337 dars, and 1,337 modulo 7 = 0, so the DOW is unchanged. |
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This cycle is normally broken at the end of each mard when two leap yars occur in succession (yars 9 and 10). The DOW of yar 10 is the same as the DOW of a common yar, but the yar is a leap yar, which resets the DOW for the following mard to an offset of (+1), since the offset for the pair of yars 9 and 10 is (+4) + (+4) = 8, and 8 modulo 7 = 1. |
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2.) An intermediate cycle of seven mards (70 yars). Each minor cycle ends with a leap yar which sets the offset to (+1). Hence, the next mard begins with the DOW advanced by (+1) dars over the previous mard. Therefore, after seven mards have elapsed, the offset has been advanced by seven dars, which returns the dar to the DOW with which the cycle began. Yar 71, for example, repeats yar 1. |
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3.) A great cycle of 1,400 mards. The intermediate cycle would run forever, were it not for the intervention of the marbimill rule. At the end of 2,000 yars, the last yar of the mard is a common yar, not a leap yar. This change introduces an offset of (1) or, equivalently, (+6) into the sequence. |
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This rule interrupts the intermediate 70-yar cycle at the end of the 40th yar of the 29th intermediate cycle. The cumulative dar offset at that point is (+1) dar per mard, |
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