Forgetting rate

The speed of forgetting. In 1885, Hermann Ebbinghaus discovered exponential? nature of forgetting. We can roughly describe forgetting with R=e^{(-S t)} where R is [memory retention]?, S is relative strength of memory and t is time. For this reason, strength of memory (S) is the best way to represent the forgetting rate. If you learn a foreign word today, in most cases, you stand only 90% chance to remember it after several days. Rate of forgetting decreases after each repetition, esp. if the repetition is made at the "right" time