(edit: to avoid some possible confusion, when I mention decay rate in this post, I'm talking about score within a given game from highest score to lowest score; not about the decay rate for scores from older games listed on the Rankings Tables.)
I think the original formula used was:
x=100x(540 - player_turns)/(540 - fastest_turns)
This formula decays to 0 at turn 540 (2050 AD), but the decay rate varied depending on the fastest_turns for each VC; e.g. assume a 350 AD Domination win vs a 1300 AD Space Race (turns 150 and 250, if I counted correctly
), players submitting 50 turns after each of these dates would score 87% and 82% respecively. I expressed some concern that the slower decay rate would draw people to the early Victory Types, reducing the potential # of players attempting later Victory Type games.
Current Formula from AlanH's webpage is
x=100x(540 - (player_turns - fastest_turns)/540
This enforces a constant decay rate without regard for VC or fastest_turns date; however, the minimum score for someone submitting a 2050 AD game would be 28% and 46% respectively for the two cases above. This seems somewhat unsuitable; the accomplishment of the fastest submittal for each VC is diluted, and to guarantee close to a 50% score for just submitting a poor later victory performance will reduce the utility of such a table.
To accomplish both a constant decay rate regardless of VC, reward Fastest Finishes, provide some measure of performance for slower submittals and put in a floor for lowest scoring winning game, I've come up with this awkward two line formula:
x=5+(45*(540 - player_turns)/(440 - fastest_turns))
if ((player_turns - fastest_turns) < 100) x=100-((player_turns - fastest_turns)/2)
The 2nd line decays scores evenly, regardless of VC, from 100% to 50% over the 100 turns after fastest_turns (in our earlier example, 350 AD Domination win is 100%, so a 1300 AD Domination win would be 50%; and 1300 AD Space Race win would be 100%, so a 1770 AD Space Race win would be 50%). Wins submitted after fastest_turns+100 would score by the 1st line; this line puts a floor of 5% in for lowest possible score, and decays evenly from 50% at fastest_turns+100 to 5% at 2050AD. This reinstates the problem with differing decay rates depending on how early the fastest_turns is for each VC, but the diffence is reduced (wins submitted at fastest_turns+150 for the two examples would score 42% and 38% respectively) and pushed out into the lower 50% of possible score.
For a fastest_finish within 100 turns of 2050, the subsequent scores (if any) would be artificially high. I have hope that implementation of a rankings system focused on fastest_finishes for all VCs would prevent that from happening (by increasing participation in all VCs), but its really no worse than giving an award to a 2050 AD milked game that decided to finish with Conquest rather than Histographic (which I think happened at least once.)
The faster decay rate over the first 100 turns after fastest_turns should help accentuate the performance of those who submit at or close to the fastest_turns for a given game. Obviously any of the parameters can be tweaked, and by all means, I would be happy to see a less awkward formula that accomplishes similar scoring method, if someone comes up with one.