http://monerotoruzizulg5ttgat2emf4d6fbmiea25detrmmy7erypseyteyd.onion/nb-no/2021/09/20/post-mortem-of-decoy-selection-bugs.html
Then, the algorithm divides the expected output age in seconds by the average seconds spaced between each output observed over the trailing year, in order to arrive at the output in the chain that should be used as a decoy. If the number of outputs in a year is equivalent to the number of seconds in a year, then the average seconds spaced between each output over the year is 1.