@KirAsh4
I finally got it running. It turned out that the sync.- problem is well known since May 2016.
–> https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=149221
sudo systemctl stop ntp
sudo ntpdate-debian
sudo systemctl start ntp
sudo ntpq -p
Now I´m happy!!
@yawns
I have already contacted myspiegel a couple of weeks ago and they told me that their mirrors are not suitable for this project. According to them the glas materials is too dark. I think they received a lot of calls the last couple of months since this project was described on german television (“Galileo”).
The only supplier I found in Stuttgart was Glass Flüss: http://fluess-glas.de/
Guess I paid ~ 80€ for 50 x 50 cm. Hope that helps a bit.
A bright screen could be a solution. I must say that I did not test the mirrors of Myspiegel.de since I found a good solution in a local shop here in Stuttgart.
I did not make the experience that it is difficult to get a mirror in Stuttgart. But the prices the local glazier would have charged me for a 50 x 50cm mirror were around 150€! I found out that most glazier here do have the same sub supplier, called a glas shop (Google: Search for Glasgroßhandel + city). So I organized the address of the sub supplier (for Stuttgart: http://fluess-glas.de/), gave them a call and asked them, whether it is o.k. if I purchase the mirror directly from them. It ended up that I payed 80 € for the mirror, and it works excellent!
Steff: If worse comes to worst there is a glas shop 100km away from Munich in my home town in Ulm: http://www.glastroesch.de/glas/540-spionspiegel.html