As you move through the series, the puzzles get more difficult, at least in theory, although that may vary based on experience and aptitude with certain puzzle types. Also, the terrain in which they are hidden tends to increase in difficulty.
To solve the Numbrix puzzle, fill in all blank squares so they make a path in numerical order from 1 to 81. You can work horizontally or vertically in any direction. Diagonal paths are not allowed.
Final Coordinates: N 30° 2A.BCD W 097° 4E.FGH
A = D2-F5-H4
B = (A6/G8)+E7
C = B4-F2-F9
D = A2-H6-E4
E = D4-E3-G7
F = C5-C3-D8
G = (G4-I4)*E5
H = C7-B8+D7
When you find this cache, make sure that you record the two clues that are attached to the log at each cache. Without all of these clues, you will not be able to solve the final bonus puzzle.
You can validate your puzzle solution with certitude.