larryd:
Your numbers do not appear correct.
Yeah i know, but i did the measurements again twice, and it is constant...
( of course, i have switched the 20kohm resistor for 2kohm, and the 10kohm for 1kohm, but still... )
Please show us a 'good' image(s) of the wiring.
Confirm measurements with a DVM.
.
I'd question the reliability of those figures. They may shift on a cloudy day.
Even better than a photo, i made a fritzing sketch :
https://img15.hostingpics.net/pics/369443Sanstitre.png