Chalk Cartridge is a marker with different color tips. It works as a mechanical pencil, that you can change easily the color by pressing the area of the eraser at the top.
This product is ideal for color coding drawings for different tasks or measurements, as in Sewing with Color products.
Always test in a scrap of fabric to check if changes the color of the fabric when erased. I have used this product for about a year and found it very useful.