MUMPS - Epoch Choice

Epoch Choice

In MUMPS, the current date and time is contained in a special system variable, $H (short for "HOROLOG"). The format is a pair of integers separated by a comma, e.g. "54321,12345" The first number is the number of days since December 31, 1840, i.e. day number 1 is January 1, 1841; the second is the number of seconds since midnight.

James M. Poitras has written that he chose this epoch for the date and time routines in a package developed by his group at MGH in 1969:

I remembered reading of the oldest (one of the oldest?) U.S. citizen, a Civil War veteran, who was 121 years old at the time. Since I wanted to be able to represent dates in a Julian-type form so that age could be easily calculated and to be able to represent any birth date in the numeric range selected, I decided that a starting date in the early 1840s would be 'safe.' Since my algorithm worked most logically when every fourth year was a leap year, the first year was taken as 1841. The zero point was then December 31, 1840.... I wasn't party to the MDC negotiations, but I did explain the logic of my choice to members of the Committee.

(More colorful versions have circulated in the folklore, suggesting, for example, that December 31, 1840 was the exact date of the first entry in the MGH records, but these seem to be urban legends. Another legend is that the date was chosen to commemorate the first use of ether as an anesthetic at Mass General.)

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