Paul Gilmartin writes: <begin extract> STCKE is notionally closer to TAI than to UTC in that TAI and STCKE are continuous timescales and UTC is discontinous. TAI and STCKE both embody the notion of (micro)seconds since an epoch; UTC is specified in terms of yyyy mm dd hh mm ss.fraction with minutes varying in length as leap seconds occur. </end extract>
Note quite. This formulation is plausible by analogy with the notion that the Gregorian Month of February, normally comprised of 28 days, is comprised of 29 days in leap years. Leap seconds, however, are inserted into UTC by the BIPM upon the recommendation of the IERS (Earth Rotation and Reference Systems Service); and they are conceptually and by definition extracalendrical. Neither 1) the last minute in June or the first minute in July nor 2) the last minute in December or the first minute in the subsequent January is lengthened when a leap second is inserted between them. [This decision was taken advisedly. There are a number of calendars---The Hebrew religious one is the obvious example---that make no use of minutes and/or seconds.] I am not sure how seriously Mr Gilmartin's means his distinction of units is to be taken; cgs [centimeter-gram-second] units and fsf [furlong-stone-fortnight] units are, I suppose, more and less perspicuous; but as long as they are unambiguously interconvertible the choice between them poses only issues of taste not substance. John Gilmore, Ashland, MA 01721 - USA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
