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 In cell A7, enter an COUNT formula, to count the numbers in column A: =COUNT(A1:A5) 2  Press the Enter key, to complete the formula.  The result will be 3, the number of cells that contain numbers. Cell A1 isn't counted, because it contains text.