Probably the subject a little bit miss informative. But not sure how to formulate it better..
Actually I stuck at point where I have to draw a path which coordinates use sqrt(Xem) like
\draw (0,0) -- ({sqrt(2)},1);
It works, but I need to calculate square root from 2em and not from 2cm as it calculates by default. I tried to add "em" everywhere it would make a sense, but it just didn't worked...

I just can not figure how to do that?
Yes, I can just use calculator and make it
\draw (0,0) -- (1.414em,1);
But it's just too rude...