Hi Ditto,

MoI can use maths functions as input values also, so you can use the circumference of a circle formula C=πxd transpose it to d=C/π and to input your example into MoI you would write it as 57/pi which will equate to a 18.144 diameter circle.

There are another maths functions that MoI uses here-> http://msdn.microsoft.com/en-us/library/shydc6ax.aspx

Cheers