The Number Lab's Vertical Number Line is a great model for teaching subtraction. Kids more readily understand the concept of subtraction when using a number line that moves vertically. Our number line is an "open number line" (i.e. you write in the numbers depending on the problems being discussed). It is made of heavy vinyl that has a sticky backing that clings to windows, doors, and smooth walls. It is easily removable and you can use dry-erase markers on it. The Vertical Number Line is 4 feet long x 1 foot wide and ships rolled in a cardboard tube.