ISNUMBER (Primitive Spread Function) tests for numeric data.

SYNTAX:

ISNUMBER(value)

REMARKS:

Returns 1 (True) if the value argument is or refers to a number. Returns 0 (False) if the argument is or refers to a value that is not a number.

You might want to use the ISNUMBER function to test whether cells contain numeric data before you perform mathematical operations on them, such as averaging the cells' contents. 

EXAMPLES:

ISNUMBER(B3)
ISNUMBER(12) = 1 (True)