For pattern markings for hems, buttonholes, darts, pleats etc. Mark fabric lightly and remove all marks before pressing. After removing the empty chalk cartridge, it is easy to reinsert a replacement. There is a plug on the new cartridge that you need to remove, then holding the chalk wheel so the empty opening is on the bottom, place the new cartridge inside the wheel. You need to hold the wheel this way so the new chalk will not spill. Once it is inserted, moving the wheel should release the chalk for marking.
