It is but reiteration to observe that once a skill has been acquired or a problem solved, the second attempt at that or a similar task will be accomplished with greater efficiency, lesser expenditure of time or effort, or both. Such improvement may be due either to memory or transfer of training-memory when repetition of the same performance is requested at a later date, and transfer when a different but more or less similar task is to be done. Memory is commonly measured by one of two principal ways: by amount retained, and by relearning. The latter method gives an index of retention in terms of saving, or economy, of time or some other measure over the score for the original acquisition. After a certain lapse of time, the subject is asked to bring again to perfection the material he once had learned. Relearning has often been claimed to be the fairest means of estimating retention, because, it is said, many elements may on the first relearning trial be subliminal, yet will come back to the subject so readily after one or two promptings that it would be unfair to assign him a zero memory score on these elements. The rapid reacquisition is evidence that he has retained them, but not clearly enough to reproduce them unaided without a little review
