sidereal time

If the clock gains or loses with respect to sidereal time, take this into account in the value of U.

When the hour circle passing through Sirius coincides with the meridian, the sidereal time is 6h.

The sidereal time at any moment is the right ascension of the hour circle which at that moment coincides with the meridian.

Having set the clock approximately to sidereal time, observe one or two more stars in the same way as above.

Sidereal time was determined by observing transits of stars over a meridian line actually laid out upon the ground, etc.