A sundial in a glass!

1. Place the glass flat, with the eyepiece facing the Sun.
2. On the side oppposte to the Sun the shadow of the eyepiece should fall on the markings on the dial. Turn the glass slightly so that the shadow of the eyepiece falls within the column for the month. If it is 1 September, the shadow of the eyepiece should straddle the vertical line separating August and September.
3. Locate the position of the shadow of the eyepiece on the wavy lines around the glass. Follow the curve back to the start. Read the time.

Note: the glass indicates solar time. To find out the standard time, you need to make three adjustments (summer time/winter time, longitude offset and equation of time).

Or… use a Papophoplon!