hen
·As he's holding a sextant I would guess is that one runs in sidereal time. That would cut out one stage of the calculations following taking a sun-sight.
Sidereal time is based on when the vernal equinox passes the upper meridian. This takes approximately 4 minutes less than a solar day. Sidereal time is useful to astronomers because any object crosses the upper meridian when the local sidereal time is equal to the object's right ascension.
I just have to Google half this answer then maybe I might have an idea of what the h... this is about. 😕