WOW this is a tricky one, and the different size circles doesnt help!
I think that the key at the bottom says that the pattern is as follow:
1 .Circle moves up from bottom right to top right, then top left (minus one) down to bottom left. (15 position + 14 positions)
2. Circle moves from top right minus one position to bottom left (minus one position) and then from top left to bottom right minus one position. ( 14
+ 15)
There is no top left to top right movement.
There is no bottom left to bottom right movement.
Using this i got some letters which yielded either SERVER, FINDING, SECRECY or WARFARE in a decryptor. This could be a coincidence though.
I have to go training now...