Thank you all for your answer.

Regarding the 100 Radius Arc, I have understand why I was not able to do 100 precisely, it was because I had the snap to grid active, so of course according to the grid it was not possible to get 100.

@French_Pilou
for the 100 arc, I was doing it using the tan method, what is strange is that I could get 99.35 or 100.6 by drawing, but if I entered 100 as D value, the arc was completly different as the one I was drawing.

I will try it again to night.

Thank you all for your help.