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.
To count positive numbers in a range of cells, you can use the COUNTIF function. In the generic form of the formula (above) rng represents a range of cells that contain numbers. In the example, the active cell contains... Count cells equal to either x or y.