A long time ago, I had to use TSO on a daily basis. One of the parts of the login process was being told the last time you logged in – you were supposed to check the last login time and make sure no one was using your account covertly, but I never bothered, partially because the date in the login message was presented as a so-called Julian date (yy.ddd). It was easy enough to figure out the human-friendly date in January, and even in February or March (especially in a leap year), but by the time April started, my interest in converting day 103 into the 12th or 13th of April (depending on whether it was a leap year) was zero. I’m sure someone made the decision to use the Julian date for a reason, but it never made any sense to me.
I was reminded of this today when I saw that the restroom cleanliness form at the place we had lunch had “1–14” as the date; I wonder if the person who set it up had been a mainframe user at one point.