Peterson Instruments stocks a wide variety of circular charts and strip chart and pens (series 39 pens and series 72/79pens) in Graphic Controls and Dri Flo II™ Brand for various makes and models of mechanical and electronic recorders. For price and delivery of charts and pens for non-gas measurement industrial recorders please call or email us as we stock too many to list here and our stock is changing daily. Graphic Controls pen description and pen part number system explained here. When ordering pens they can be ordered by OEM pt #, Graphic Controls pt#, or Dri Flo II pt#.