Why does excel use different denominator for variance and covarian
 

Ales wrote...
Why does excel use different denominator when calculating variance and

covariance? When working with samples it should be "n-1" in both
cases. Just
"n" when calculating covariance is by my humble opinion wrong.

There are a few sources that don't agree with you, e.g.,

http://documents.wolfram.com/applica...ies/1.5.1.html

But there are others that do. So it appears to be due to some ambiguity
in what's intended that doesn't originate with Excel.