The curve for sending, aside from minor irregularities, rose with a fairly smooth sweep, tapering off finally towards the "physiological limit", the limit of what the nerves and muscles of this individual could perform. [Footnote: A good example of the physiological limit is seen in the hundred yard dash, since apparently no one, with the best of training, can lower the record much below ten seconds; and any given individual's limit may be considerably worse than this, according to his build, muscular strength and quickness of nerve centers. The simple reaction gives another good example; every one has his limit, beyond which no amount of training will lower his reaction time; the neuromuscular system simply will not work any faster.] The receiving {322} curve rose more slowly than the sending curve, and flattened out after about four months of practice, showing little further improvement for the next two months. This was a discouraging time for the student, for it seemed as if he could never come up to the commercial standard. In fact, many learners drop out at this stage. But this student persisted, and, after the long period of little improvement, was gratified to find his curve going up rapidly again. It went up rapidly for several months, and when it once more tapered off into a level, he was well above the minimum standard for regular employment. Such a flat stretch in a practice curve, followed by a second rise--such a period of little or no improvement, followed by rapid improvement--is called a "plateau". Sometimes due to mere discouragement, or to the inattention that naturally supervenes when an act becomes easy to perform, it often has a different cause. It may, in fact, represent a true physiological limit for the act as it is being performed, and the subsequent rise to a higher level may result from _improved methods_ of work. That was probably the case with the telegrapher. [Footnote: A plateau of this sort is present in the learning curve for mastery of a puzzle, given on p. 316.]