Calculating wrong dimensions

[mrbmason]

Hi,

I just purchased and downlaoded HomeDesinger Suite 2014 and I am trying to create a design that matches my existing house. I have the original blue prints
One wall shows an outside dimension of 22' 2". The outside walls are 10" thick. I have successfully added those to my floor plan. The trouble comes when I try to add an interior wall that is 5" thick. The blue prints state that it is 9' 6" from one wall and 10' 7" from the other which adds up if I do the math by hand. But in my floor plan if I make the wall 10' 7" from one side the other dimension is calculated at 10' 4 7/8" almost 11" too much. How could this be?

Thanks,

Brian