I found an neatly-edited article about Gun Milap on the web. The unique thing it teaches on how to calculate the individual Kutas as well, besides a sum of all 7 of them. Take a read by clicking here.
Some of you may not believe in these things at all. I respect your opinion that way. But, I must say that many ancient jyotish calculations are based on very accurate calculations based on movement of planets. In high-school we study about the gravitational forces, depicted by constant 'G'. So, at least, believe that big bodies do influence other bodies in this universe. Interestingly, Vimshottari dasha is also calculated based on such influences. If you want to do some research on it, you will find out how it is calculated. Most pundits agree that Vimshottari dasha is one such calculation that is very close to being amazingly accurate, if analyzed properly.