Trouble with the rectangel tool.

Hello,

Can someone pleas help me.

I am new at using DS.

I am trying to draw our upper floor ,hit some troubled when I was almost ready.

Now when i use the rectangel tool and say that i whant it to be 10 by 10 and messure it it can be anything betwen heven and earth.

If I open a new drawing and try it will do the same.

If I use the circel tool the messure gets correct.....

What have I done?????

 

Greatful for some help.

Stefan