How to play Calcudoku
Calcudoku combines the row and column constraints of Sudoku with numerical regions that are similar  but not identical  to those in Killer Sudoku. To solve Calcudoku, place the numbers 1 to 6 (or whatever the width of the puzzle is) once each into every row and every column. Further, the given value at the topleft of each boldlined region must be obtained when all of the numbers in that region have the given operation (+, , ×, ÷) applied between them. For  and ÷ operations start with the largest number in the region and then subtract or divide by the other numbers. In Mystery Calcudoku a '?' is given instead of an operation. In these you must work out the operation too  at least one of adding, subtracting, multiply or dividing results in the given total. Note that there is no constraint on repeating numbers in boldlined regions  calcudoku is different to jigsaw sudoku and killer sudoku puzzle in this respect. To help understand the fundamental rules, consider the "1" region at the topleft of the puzzle below. The two numbers in this region must result in 1 when the "" operation is applied between them, with the smaller number subtracted from the larger. Therefore possible solutions to this region are 1 and 2 (since 21=1), or alternatively 2 and 3, or 3 and 4, or 4 and 5, or finally 5 and 6, and these could be written in either order into the two cells.
We can start solving this puzzle by writing in a few of the possible solutions to the numeric regions, beginning with some of those which have only one possible pair of digits. For example the "20×" in the top row can only be solved by 4 and 5 (4×5=20):
Note the cell in green. There must already be a 4 and 6 in this column, and since numbers cannot be repeated in a column we know this must be a 5. This also means there is only one solution to the 9+ region at the bottomright now:
Because we must have each number from 1 to the size of the puzzle (6 in this case) in each row and column, we now know that the toprightmost cell in the grid must be a 1. This in turn lets us complete the 3÷ region that this 1 is now in with a 3, since 3÷1=3, and we also now can narrow the 2 and 6 in the top row down to two possible cells:
Notice how the green cell has three possible options to the two above it. This is because the possible solutions involving the 2 and 6 we have already placed are 65=1, 21=1 and 32=1  i.e. the 1, 3 and 5 that are now options in that cell. We can make several more deductions in a similar fashion, for example that the 2× in the bottom row must be solved by 1 and 2, and the elimination of the 3 from the rightmost cell in the 3× region now that we have a 3 in that column already:
The cell marked in green is part of a 2 region. To use the 5 candidate the solution would need to be 53, but the 3 would share a row with an alreadyplaced 3, so the solution must be 4. This in turn lets us complete more of the top row of the puzzle:
From here we need only make similar steps and soon we will have completed the entire puzzle:
Calcudoku makes use of many of the same tricks that you will use on Sudoku and Killer Sudoku, but don't forget that numbers can repeat in boldlined regions. This means, for example, that a 6+ region of 3 cells could be solved by 1, 1 and 4 (so long as the region was Lshaped, otherwise the row or column constraint would prevent the repeat).
