A

grid puzzle in which each cell in the grid is occupied by a

digit 1 through 9 (0 is not used).

The same digit is never used twice in an entry, and the sum of each entry is given in a black square to the left of or above the entry (a la Pencil Pointers). A diagonal line divides the black square when it must hold two sums.

Because of these rules, it is often the case that you can determine which digits must go in an entry from the length and sum alone, but you will need to use information from crossing entries to determine which digit goes where. For instance, the only fill for a 3-digit entry that adds to 7 is 1, 2, and 4 in some order.

Two-digit entries are common, unlike two-letter words in crosswords.

A related but somewhat less common variant is Cross Products.