Computing the duration of the period between two UTC times, using SRFI-19 mechanisms:
scheme@(guile-user)> (use-modules (srfi srfi-19)) scheme@(guile-user)> (define t0 (date->time-utc (make-date 0 59 59 23 30 6 2012 0))) scheme@(guile-user)> (define t1 (date->time-utc (make-date 0 1 0 0 1 7 2012 0))) scheme@(guile-user)> (time-difference t1 t0) $1 = #<time type: time-duration nanosecond: 0 second: 2> The two times are 2012-06-30T23:59:59 and 2012-07-01T00:00:01, so at first glance one would expect the duration to be 2 s as shown above, the two seconds being 23:59:59 and 00:00:00. But in fact there was a leap second 2012-06-30T23:59:60, so the duration of this period is actually 3 s. The SRFI-19 library is aware of this leap second, and will compute the duration correctly if it's translated into TAI: scheme@(guile-user)> (time-difference (time-utc->time-tai t1) (time-utc->time-tai t0)) $2 = #<time type: time-duration nanosecond: 0 second: 3> The original computation in UTC space should yield a result of 3 s, not the 2 s that it did. Since 1972, the seconds of UTC are of exactly the same duration as the seconds of TAI. (They're also phase-locked to TAI seconds.) Thus the period of three TAI seconds is also a period of three UTC seconds. It is not somehow squeezed into two UTC seconds. -zefram
