For some 400 years, the pocket watch was the most popular form of portable timepiece, only surpassed by the wristwatch in the 20th century. From the 16th century onwards, the pocket watch became an essential accessory for men, being both practical and fashionable with the development of elegant designs. Traditionally, the pocket watch is fastened to a chain, enabling the clock to be worn as a necklace or secured to a part of clothing. Whilst Europe has been manufacturing since the 1500s, the first American pocket watches were not produced until the 1800s. Despite the slow advancement in the States, the Waltham Watch Company of Massachusetts were the first to develop pocket watches with interchangeable parts, both speeding up the process of manufacturing as well as reducing the cost. Waltham pocket watches are still highly coveted by horological enthusiasts today, with many being sold by dealers and at auction.