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.
This scenario is preferable to seeing #VALUE! if the cell doesn't contain a number. In this case, I'll use Excel's IF function combined with the ISNUMBER function to get the right outcome. Suppose we have this example (it's a simple calculation simply to illustrate the point).