The Spot-on Sundial is easy to read. The shadow of the top slanting edge of the gnomon travels round the sundial in a clockwise direction.
This shows the shadow falling exactly on an hour line. The time is 8am winter time (indicated by the VIII Roman numerals) or 9am in Summer Time/Daylight Saving Time.
An hour and ten minutes has passed. The shadow now falls on the first of the small lines indicating 10 minutes past the hour. The time is 9:10am (or 10:10am in Summer Time).
Nine minutes later, the shadow has passed the spot indicating a further five minutes, and is considerably closer to the next ten minute line than to the spot. The time is 9:19am (or 10:19am in Summer Time).
And so we reach the time of solar noon (12 in winter and 1pm in summer) with the line of light shining through the air gap, and directly across the circle.
The Unique Line of Light
Note that the times given in this page are local times by the sun. The difference between your local time and the time on your watch depends on your longitude and the Equation of Time.