simple calculations in object property fields

Would be a great work aid if object property fields
(either in toolbar or in object properties dialog)
would accept and calculate on the fly entries
containing simple calculations, like:
X position: 28+2
Y position: 148-54.5
Width: 150%
height: 268.35/7

etc.

regards

Lukasz Oracz (lukor)
<email address hidden>

P.S. Thank to everyone who anyhow participate in
creating this extremely great app.