Prym Chalk Wheel ?Mouse? from the prym.ergonomics series contains a washable dressmaker?s chalk powder that is perfect for marking lines and notches on all types of fabrics. The small gear wheel gives you a fine, clear chalk line and the chalk level in the cartridge can be seen through the inspection window. Replacement cartridges can be bought when needed. This ergonomic chalk wheel mouse is comfortable in the hand and will give you fatigue-free use. It also comes with a snug-fitting cap to protect the wheel when not in use.