The slope of a learning curve will increase over experience (time) until it reaches a certain point at which it will become almost constant.
The learning curve was at first introduced by Hermann Ebbinghaus in 1885, as an instrument to measure efficiency in production and to assess the costs derived. The steeper its shape is, the more rapid the progress accomplished in the learning process. The steep phase entails as well larger cost savings. Subsequent learning starts to take place at a slower pace and this is translated into more difficult savings.