Using the Zudoku Program

Finding the Solution

Simple Strategies First

It is easiest to start with the simpler strategies that do not require marking the small numbers in the cells:

Only one cell is not solved in a group
Basic Intersecting groups: only one number is possible where they intersect
Linked Intersecting groups: intersections with one group place limitations on intersections with other groups that lead to only one number being possible in the latter intersection.

Intermediate Strategies

If the simpler strategies do not solve the puzzle, then you need to mark which digits are impossible in each unsolved cell.

Distinguishing between Possible (green) and Unknown (gray) is optional. Computer solving strategies treat them both as Possible. The only difference is that Possible numbers are tested for conflicts automatically or by the Menu/View/Test and Show Errors command. This can be very useful for checking your work as you go. See the Error Checking section.

Two intermediate strategies can be used manually without marking the small numbers in the cells, but are much easier if the small numbers are marked. Hints and Auto-Solve for these strategies require impossible digits to be marked in all cells:

Solve a cell with only one number possible (all other numbers have been marked impossible)
Solve the only cell in a group where one number is possible (that number is impossible in all other cells in the group)

Advanced Strategies

You need to mark which digits are impossible in each unsolved cell before using advanced strategies. These strategies do not directly solve a cell, but can mark more digits impossible which can lead to more solutions by easier strategies. The advanced strategies are:

Find Box Eliminations looks for situations where a number must be in a row or column of a box, therefore that number cannot be in any other rows/columns of that box and should be marked impossible there.
Find N-tuplets (an N-tuplet is a couplet, triplet, quadruplet, etc.) looks for N cells in a group that contain exactly N different numbers. Since those N numbers must be in those N cells, those numbers are marked impossible in all other cells of that group.
Find Hidden N-tuplets looks for N different numbers that are found in exactly N different cells in a group. Since those N cells must contain those N numbers, all other numbers in those cells are marked impossible.

Normal Solving Process

A practical approach for starting a new puzzle is to go as far as you can using only strategies that dont need the small numbers marked, then when you get stuck start marking the small numbers until you find a pattern that will get you going again.

Normally you want to start with the easiest strategies first, moving to harder strategies as necessary. Once a harder strategy has solved a few cells or marked more digits impossible, then return to the easiest strategies and work your way up again.

Taking the time to mark all of the impossible digits in all unsolved cells is a bit of an investment, but once it is done all of the intermediate strategies become easy and the advanced strategies are not that hard. Even if you return to the simpler strategies, keep marking impossible digits resulting from each new solved cell so that the more advanced strategies are still available.

If you find marking impossible digits tedious, or simply want to make sure they are all up-to-date, then use Menu/Solve/Mark Conflicts As Impossible.

Alternative Solving Approach

Another approach is to use Menu/Solve/Mark Conflicts as Impossible right at the beginning. Then you can use the more advanced strategies first. This makes it seem like a different puzzle from the normal start.