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.
In this lesson, we'll look at Excel's ISNUMBER function as a way of doing this. I was recently asked by a reader to provide a formula that would return the result of a calculation if a certain value cell contained a number, and leave the cell blank if that value cell contained anything that wasn't a valid number.