Ebbinghaus taught himself 169 separate lists of 13 nonsense syllables.

Each syllable comprised a ‘meaningless’ consonant-vowel-consonant trigram. Ebbinghaus relearned to 31 days. He was especially interested in the extend to which forgetting had occurred over this time period, using the ‘saving score’ (i.e. how much time it took him to relearn the list) as a measure of how much he had forgotten.

Ebbinghaus noted that the rate of forgetting was roughly exponential: that is, forgetting is rapid at first (soon after the material has been learned), but the rate at which information is forgotten gradually decreases.