If he selects the 4 request him to multiply by 36 and the result will be

4 4 4 4 4 4 4 4 4

Whichever figure he selects, mentally multiply it by 9 and request him

to multiply the row by the result. If he thinks 9 the most imperfectly

made figure, you, of course, tell him to multiply by 81 and the result

will be all 9's.