Hi Brian,
>>Is the calculator in-built with Windows not sufficient anyway?

Yeh that's what I use, but as this post heading says 'lazy designer'.
As a natural flow instead of dropping out of MoI and calculate something on MS calculator, then copy and paste the result back into MoI,
you could for example, say I wanted to make a box width 23.7mm, half the width for it's height and a third of the width for extrusion (if the value input had calc functions)
we could just type;
Height 23.7

Width 23.7/2

Extrusion 23.7/3

Cheers