Endless possibilities in exploring addition, subtraction, counting on and counting up to 20. How many windows do you see? Subtract the number of houses without chimneys from the total with. Low cost, roll up, front of class, teaching resource. A dry wipe plastic overlay with holes at top, to fit onto a flip chart easel. Size: L. 810mm W. 540mm. Comes with storage tube. If using over a metal whiteboard surface, then our full range of magnetic accessories can also be used See range: Home page/accessories If purchasing for use with the Learning with Linden whiteboard easel(code 1a)and overlay holder, then you will also need to purchase 2 battens per overlay. Choose - Overlay Battens: Home Page/accessories.