The Subtraction Strip Board (C 104) is a foundational arithmetic material that introduces children to the systematic memorization of subtraction facts using numbered strips on a ruled board, helping them visualize differences concretely before moving to abstraction. It belongs in the Math area for primary children approximately ages 5 to 6.5 who have completed early sensorial number work and are ready to begin the tables. Paired with the corresponding command cards and booklets, it gives children a structured, self-correcting path through the subtraction facts that they can work through independently over many sessions.