The American Optometric Association suggests that children should have their first regular eye exam at six months of age. Another vision exam should take place when a child is around two or three years of age when their vision undergoes its most rapid development and vision correction is most effective.
The ISNUMBER function is a quick, easy way to check if a cell contains a number. Our example used the IF function to illustrate how ISNUMBER can be used. If you haven't used IF in a formula before, you can read our lesson on the IF function here.
1 If the specified cell range contains no logical values, OR function returns the #Value! (its the error value)  To check whether a value occurs in an array, you can use OR array formula. However, keep in mind that you have to press the keys CTRL+SHIFT+ENTER and not simply the return key.