El sol en invierno está más bajo en el horizonte que en verano, por ejemplo en mi salón que está orientado al sur en invierno entra la luz varios metros por la ventana y en verano no pasa de 30 ó 40 cm.
He encontrado estas instrucciones en inglés. ¿No has probado a mirar la hora a las 12 de la mañana?
A Nomos Sunwatch.
The perfect Glashütte watch for sunny dispositions with a small budget. For this watch, the Glashütte watch manufacture NOMOS has developed a caliber that will bring the brand a large head start in terms of research and development. The fifth movement after Alpha, Beta, Gamma, and Delta, Caliber ETA, doesn’t need batteries and it never needs to be wound – though it is not an automatic movement: ETA is the first wearable sundial in the history of Glashütte. This watch, which functions according to the principle of the so-called farmers’ ring, is extremely comfortable, and it leaves the wrist free for other jewelry. The small NOMOS sundial is worn on a band around the neck. Its handling is very, very simple. One only need to set the approximate date on a rotating ring, let the sun shine a little, and hold the watch in its direction. The light coming through a little hole in the ring projects a dot of light onto a time scale found inside the ring allowing one to read the time. Regarding precision, the sundial can’t quite take on a mechanical NOMOS caliber. And when it’s raining, it can’t be counted on either. But, this watch is a) beautiful; b) incredibly inexpensive for a true Glashütte timepiece; and c) it is water-resistant to any depth. The ring is crafted from stainless steel and the inscriptions are laser engraved using a difficult process.
Explanation and Time Indication:
To read the time it is necessary to know the approximate declination of the sun above the horizon. Therefore set the small hole in the ring to the current month on the outer scale of the ring. Then hold the ring hanging with the hole directing to the sun so that a small dot of light is being projected to the inside of the ring where time can be read off.
This handy little timekeeper shows the true local time for all places found along the same latitude as Glashütte, 51° North. For all other places around this latitude, the time shown is approximately correct, the deviation is only a few minutes per degree latitide, this is below the accuracy of reading on this timepiece so if you are not too accuracy fanatic (in this case this timepiece won´t be eight for you anyway) you can pretty well use it on the Northern Hemisphere in a belt of ca. 40°-60°N Latitude North to stay within a tolerance of about 2 light points = ca. 1/2 hour.
On the Southern Hemisphere it is working correspondingly in the belt of 40°-60°S Latitude South - all one has to do is adding 6 months one the month scale, i.e. January = Setting Juli etc.
pero que mejor ocasión para recordar el día que descubrí uno de estos relojes. 
