From: Nicolas Martin (
Date: Tue Feb 23 2016 - 06:46:44 CST

Dear Chitrak, dear all,

thank you for your advice. I checked what you suggested. a and b are
equal and different from zero when c is also different from zero but
with a higher value.

I still think that the centering is, at least part of, the problem, but
since my selection is ok, I honestly don't see what could be wrong at
this point.

Bests Nick