The change in Elo ratings depends, among other things, on the K-factor (or development coefficient).
FIDE Rating Regulations effective from 1 July 2017 give the following values:
- K = 40 for a player new to the rating list until he has completed events with at least 30 games; and for all players until their 18th birthday, as long as their rating remains under 2300.
- K = 20 as long as a player's rating remains under 2400.
- K = 10 once a player's published rating has reached 2400 and remains at that level subsequently, even if the rating drops below 2400.
The same values have been in effect since July 1, 2014.
The Wikipedia page on the Elo rating mentions that FIDE used the following values before July 2014:
- K = 30 (was 25), for a player new to the rating list until the completion of events with a total of 30 games.
- K = 15, for players with a rating always under 2400.
- K = 10, for players with any published rating of at least 2400 and at least 30 games played in previous events. Thereafter it remains permanently at 10.
- When were these past rules enforced?
- When was the change from K=25 to K=30 applied?
- With the exception of this last change, have these values been applied since the beginning of Elo's creation?
I take the liberty of asking all these questions at once because they're related.