This tells you how to solve these darn puzzles......
Here's an excerpt..
1. Mark each cell with all the values it could possibly take (tedious but necessary, and requires a the puzzle to be copied onto a suitably-sized piece of paper)
2. Now examine each box, then row, then column and look for N cells that share the same N digits.
When you find them, then all the other cells in the box or row or column may not use those digits.
For example, if in a row the possible solutions to 2 cells are both limited to 1 or 9, then no other cells in that row may have either 1 or 9 as a solution.
These previously possible solutions may be struck out of those other cells , leaving the 2 cells with those 2 digits as allowed solutions.
Another example, if in a column 3 cells have ........." READ ON