The puzzle only uses the numbers from 1 to 9.
There is really only one rule:
Fill in the grid so that
every row,
every column, and
every 3 x 3 box
contains the digits 1 to 9.
You can't change the digits already provided in the grid.
You have to work around them.
There's no maths involved.
The grid has numbers, but nothing has to add up to anything else. You solve the puzzle with reasoning and logic.
The puzzle only has one correct solution.
Here it is -
In this puzzle you need to know what numbers go into the A, B, C & D squares. When you have them you can go to the cache at -
S 35 07.(A-D)(B-C)(C+D) E 147 21.(B+1)C(B-A)
Some might say that you would often get a mystery at this location.
The cache is now a very small container, so no swaps. BYO pencil too.
It can be a high muggle area, so please park as close as you can and beware, and then replace it carefully as it was.