So you have metric papers, your graph will be possibly a european product. We have a lot of those items running and in the ten years in this museum I remember the change of the pens only a few times, they run for years and years. If you'll send me the name of the thermohygrograph, maker and so on and perhaps the order-nr. of the papers I'll try to find out better pens. regards Gerhard Dangel-Reese Augustinermuseum Freiburg fax ++49-761-201-2597