Not the Bay of Biscay Mystery Cache

This is not the actual location of the cache, although the cache is very close.

You will need a pencil, a piece of paper (calculator optional) and a few minutes.

It's anticipated that quite a few will initially get this wrong. That said, I hope I'm mistaken.

At the given location, there's an implicit number. Multiply that number by the following pair of numbers and their purpose should become clear:

0.77981054, -0.08181009

The actual cache is a small tablock container containing a pencil, logbook and some swaps.