"Magic Skeleton" ETA 2824-2

This is a freebie for Members of the City Chain club
I was very surprised to find the ETA 2824-2 in that free membership watch. I had seen the watches many times, there is a booth in almost all of the City Chain outlets advertising the watch to potential members.
The magic about its dial is, that the disk that holds the second hand, changes the color from transparent to almost black every 15 seconds. I think the disk holding the red second dot might consist of a very smart phototropic PVC sandwich. The "timer" for the disk to become dark and transparent seems to be built-in, I could not find any signs of a contact leading to the inside of the watch. At first I suspected some electronic at works, but it seems that the disk is changing its opacity only due to its photovoltaic attributes. A truly fascinating idea!
Once the dial is almost fully transparent, the dial offers a great view to the ETA 2824-2 without the calendar mechanism.
The 5 minute indices are painted on the inside of the sapphire crystal. Finding a sapphire crystal on a freebie, that was actually the second surprise. Also the City Chain logo and the inscription Hong Kong 1997-005 are painted or etched on the inside of the front glass.