In Figure 5 which line is longest, A, B or C?
Good practice can be had in judging the size of boxes by comparing the length of one box with the width of another, or any similar measurements. In each case the measurements should actually be made so that all error can be corrected.
In the same way practice with size and thickness of books. Let the child estimate them by inches so that he learns to determine accurately the difference in thickness. The carpenter can readily tell the full inch board from the seven-eights boards by looking at it or by feeling. His ability to do this is the result of practice.
The size of type is a good thing to practice with, as the irregular outlines of the type make it quite confusing. A sample book of type can be gotten from any printer. From this the child can also be taught to become familiar with the common type faces. This knowledge he can use to good advantage in later years.
The child should be taught a definite length of step for the purpose of measurement. In proportion to his size he can learn to step off two feet or a yard. He should also know the length in inches of his shoe for the purpose of checking shorter measurements.
Have the child know his height and estimate the height of trees, buildings, etc. These estimates can be checked by computing the proportion of the length of the shadow thrown by the tree and using the proportion.
Example—If the child is five feet tall and his shadow measures three feet, the shadow is three-fifths of his height. If the shadow of the tree measures fifteen feet, the height of the tree is twenty-five feet.