The Eddington Number is the greatest number of days that you've ridden that distance. So, if you've managed 30 or more 30-mile days, then your number is 30. If you've only managed 20 or more 20-mile days, then your score is 20. It's an interesting self-improvement statistic, but is quite difficult to calculate - so here is a Strava-based tool that does it for you!
Need more background information? Read more about the Eddington Number, plus some all-athlete charts.
You can now see a breakdown of your Eddington number within each year, seeing how it increases month by month!