This is a 2-part, double puzzle. Part one is done on your computer and part two is done in the field.
For part one go to the related web page.
The solution will lead you to the first waypoint where another puzzle awaits you. Solve that one to get to the cache.
It has been brought to my attention that the in the field puzzle was reproduced with an error: U=3 is wrong; it should be U=4. Sorry for any confusion.
Please try to re-hide these well.
Congrats to mcgmarauders for FTF!!!