9.99999999999999E+307 is the biggest number that Excel can handle (just under 1 with 308 zeros behind it).
9.99999999999999E+307 is used in formulas to find the largest value that is less than or equal to the search value. Because
9.99999999999999E+307 is an impossibly large value, the formula finds the previous numeric value.
You can probably use a smaller number than
9.99999999999999E+307, but make sure it is bigger than any number you might use in your file, for examlple, you can use
9.9E+307 is not recommended.
9.99999999999999E+307 is often used with LOOKUP, MATCH, VLOOKUP or HLOOKUP function. For example:
Find the position of the largest value
The values in the lookup_array argument must be placed in ascending order.
Find the largest value