The Parker Jotter is the Parker Pen Company's second and best-selling retracting refillable ballpoint pen. The first was the Hopalong Cassidy ballpoint. (Later a fountain pen, mechanical pencil and rollerball pen were introduced to the line). Since 1954, over 750 million have been sold worldwide. It is priced between $6 for lower end models, and $20 for higher end models, such as special editions. Its refill has a ballpoint tip originally called the T-Ball (for Tungsten), with a unique textured surface that greatly reduces slipping and failure to transfer ink onto slick paper, known as "skipping." The technology is now commonly used in the pen industry. The pens are also a popular advertising medium. The external design of the Parker T-Ball refill is a configuration copied by many other brands of refillable pens.