Hello, Judah Levine, I get unexpected results on Linux with TZ=right/Universal. I downloaded https://data.iana.org/time-zones/releases/tzdata2018g.tar.gz to try to find an explanation. There, I find, in: leap-seconds.list ... # # Updated through IERS Bulletin C56 # File expires on: 28 June 2019 # #@ 3770668800 # 2272060800 10 # 1 Jan 1972 2287785600 11 # 1 Jul 1972 2303683200 12 # 1 Jan 1973 2335219200 13 # 1 Jan 1974 2366755200 14 # 1 Jan 1975 ... I tend to believe this, but in: leapseconds ... # There were no leap seconds before 1972, because the official mechanism # accounting for the discrepancy between atomic time and the earth's rotation # did not exist. # The correction (+ or -) is made at the given time, so lines # will typically look like: # Leap YEAR MON DAY 23:59:60 + R/S # or # Leap YEAR MON DAY 23:59:59 - R/S # If the leap second is Rolling (R) the given time is local time (unused here). Leap 1972 Jun 30 23:59:60 + S Leap 1972 Dec 31 23:59:60 + S Leap 1973 Dec 31 23:59:60 + S Leap 1974 Dec 31 23:59:60 + S ... Well, it's consistent with itself. 1971-12-31 23:59:60 is *before* 1972. But "leap-seconds.list" shows one more leap second that "leapseconds". I'm confused. Thanks, gil