I bowl in a Petersen singles league, and we use decimals for pinfall. We also use a 6-week rolling average and a 10-pin maximum average drop from the previous season.
For instance, let's say it is the first week of league and handicap is established as 100% of 230. My incoming average is 220, I bowl 690, and I beat my opponent 2 games and total. The scoring for that week would look like this:
690 scratch pins plus 30 handicap pins = 720
720 / 50 = 14.40
14.40 Petersen Points plus 3 match points = 17.40 total points for the week.
Now since we use a 6 week rolling average and the following week is only the second week, we use a formula to calculate the rolling average.
(total pinfall) plus ((18 - total games bowled) * incoming average) / 18 = rolling average
So in this case it would be:
690 plus (15 * 220) / 18 = 221.
Wash, rinse, repeat! Hope this helped.