Working Through 6x6 Grids
Every row and column of a 6x6 grid adds up to 21, a total worth using when only one or two cells of a row remain. Look for cages with one combination: two cells adding up to 11 hold 5 and 6, a difference of 5 can only be 1 and 6, and two cells with a product of 30 hold 5 and 6.
The Three Sets of Operations
On addition-only sheets, every cage is a sum. Addition and subtraction sheets add two-cell cages whose number is a difference. All-operations sheets also use products, on cages of two or more cells, and quotients, on cages of two cells whose larger digit is a multiple of the smaller.
Printing and Format
Each sheet holds its four grids on A4, in black and white, with cells large enough for a digit and a few notes; the 6x6 Calcudoku page prints a single grid on each sheet instead.