No, the 1E10 is the lookup_value.
1E10 = 10,000,000,000 (10 billion)
The way that LOOKUP works is if the lookup_value is greater than any value
in the range then it returns the *last* value that is less than the
lookup_value. To insure that we get the *last* number in the range we use an
arbitrary huge number like 10 billion. If you we working with numbers that
big then we just use an even bigger number for the lookup_value like 1E100.
I don't even know what that value is called! <g>
Consider this example. Suppose you were working with bowling scores. The
highest possible bowling score is 300. In this case we know for certain what
kind of numbers we're dealing with so we don't need a huge arbitrary
lookup_value like 1E10. We just need a number that is guaranteed to greater
than 300. So, we can use 301.
=LOOKUP(301,A:A)