Scid has a number of graph features, displaying information about Player Ratings, Game Frequencies and Score Evaluation.
Relative Filter Graph
Absolute Filter Graph
The iconic button near the bottom opens a dialog to configure the graph. You can select the range and interval for the X axis. The "Decade" criteria can't be configured, use "Year" instead. If "Estimate" is selected, a missing rating will be estimates as described below. Otherwise no estimation is done and missing ratings are count as zero. This matches the Min. Elo evaluation in the statistic-window.
Note: the calculation can take some time on large ranges and small intervals.
When plotting the Filter graph by rating, Scid uses the average rating for each game. Estimate ratings (such as those in the spelling file) are not used. If one player in a game has a rating but the opponent does not, the opponent is presumed to have the same up to a limit of 2200. For example, if one player is rated 2500 and the opponent has no rating, the mean rating is (2500+2200)/2=2350.
The first step in using the Score Graph is to add scores to a game with Scid's annotation feature. These scores have one of the formats +0.25, [% +0.25] , or [%eval +0.25]. The later two formats allow these scores to be hidden in the PGN window by enabling PGN-> Hide Codes. The values are represented from White's perspective (so a negative value means black is ahead). In cases when the scores are not from White's perspective, one can select an option (in the Options Menu) for an inverted perspective.
Left Click positionally in the graph to go to the corresponding move.
Right Clicking anywhere in the score graph will perform a refresh.
The current move is now highlighted a different colour, though for performance reasons (on OS X mainly), this can be disabled.
It is also possible to change the Graph colour via