"Even" is a difficult word for pattern discussions.  Most will interpret it as the "pegboard" distribution.  Fortunately, the Rayleigh distribution is both center rich in pellets and the pellets there are the slowest spreading.
We could use "even" as follows.  Assume an in-flight clay target is seen about half way between edge-on (5 sq in) and face-on (15 sq in) and exposes 10 sq in.  For this presentation, one way to analize it would be to make a series of concentric "washers", each of 80 sq in.  Now, divide each washer into eight "pie" sections.  Count the number of pellet strikes within each "pie" section. Average all eight and you have the average number of pellets that are likely to strike a target at the average radius of the washer (aiming error).  Now, compare the numbers within the pie sections.  If each of the eight pie section had the same number of strikes, we could say the pattern was "even" at that radius.  Repeat from center to "as far out as you care to go."  Repeat for ten patterns.  At this point you have some real, statistically sound data.  Once you become accomplished at counting holes, you can do a pattern in about 15 minutes/2 1/2 hours per set of ten 

.  OR, you could learn to use Dr. Jones's computerized method. 

DDA