Fits of two equations proposed by Ebbinghaus in 1880 and 1885 to data from his own study and from three replication studies.

See text for the meaning of the parameters. SSD is the sum of squared differences between data and fitted curve, R2 is proportion variance explained, and AIC is the Akaike Information Criterion. To stay close to Ebbinghaus’ own estimates, the parameters are fitted for time expressed in minutes.