An Easy Heuristic to Explain Month-To-Month running differences

 This month I ran 100.5 miles in 15:54:45 and last month, the exact same distance at 15:35:38 and I wondered if there was a quick way to inspect the monthly workouts to explain the difference.

Here is what I came up with:  I normally run in the mid 9-minute per mile range, so add a point for any run at or above 9:45 and two points for any run above 10:30, but subtract 1 point for any run below 9:00.

In October, I score 4 points:  3 9:45 or more, 1 10:30 or more and one below 9:00.  In September the score is an even 0.  Four were above 9:45 and 4 were below 9:00.

Each point is worth 5 minutes.