Hi Burr, no problem!
Did that make sense for how to use that formula inside of MoI?
Just in case here is a stepbystep for how to use it.
Say you want to create an arc of radius 5.5 that has a length of 8.1 units.
To begin with, start the Draw curve / Arc / Center command.
Pick the center point somewhere that you want to place the arc at.
For the start point of the arc, type in 5.5 <enter> to activate distance constraint. That will make the next point you pick be constrained to be 5.5 units away from that center point, that is how you set a specific radius value when drawing an arc with that particular arc tool.
Then click to place that start arc point.
Now the Arc command will be at the prompt that has an Angle: value you can enter.
This is where you enter that forumla  to enter it press the Tab key to put keyboard focus into that Angle box (if you enter numerals your focus will go there automatically but since we are entering an expression that starts with a parenthesis character it won't go there automatically so hit tab to do it).
Then you type in the formula: (8.1 * 180)/(5.5 * PI) <enter>
So note there that I used this formula: (Length * 180) / (Radius * PI) but replaced the Length and Radius with the specific values for length and radius that you want to create for this arc.
So those steps above will make an arc that has a length of 8.1 units.
 Michael
