Help on Radial health bar (Hollow Circle)

I am trying to create a circular health bar in gmod for my server. I like the look of it, i just don’t know how to do the math/make it draw the shapes correctly with the math. Basicaly, i want this:

(I have no idea if the image worked)

Obviously with the blue bar being Armor and Red being HP.

Couldnt find the original post but you can use the code from thid. http://forum.facepunch.com/showthread.php?t=1524258&p=50582620

Alright, Thank you.