Octisum

OCK-ti-sum  ·  octo + summa

Eight arrows. Every line adds up.

Place compass arrows so none repeats in a row or column, and every line adds up to the pair beside it.

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About Octisum

Octisum (OCK-ti-sum) comes from Latin octo, eight, and summa, sum: eight arrows, and every line adds up.

Each compass arrow is a vector: → is (1, 0), ↗ is (1, 1), and so on around the compass. Fill the grid so no arrow repeats in a row or column and every line adds to the pair printed beside or below it. Puzzles run from quick 3×3 warm-ups to 5×5 grids with extra clues between squares. Each one has exactly one solution, and you can reach it by logic alone, without guessing.

You don't need to know any vector maths. If you like Sudoku, KenKen or Kakuro, you already have the instincts.

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