Charles Terwilliger attended Phillips Exeter Academy and the Massachusetts Institute of Technology and worked for many years in market research, promotion and sales in the magazine advertising field. He became interested in clocks, particularly the 400-Day Clock and, after observation and study, developed the Horolovar Temperature Compensating Suspension Spring for it, which resulted in the first improvement in the clock's timekeeping in the 70 years since its invention. He also wrote a repair manual, the Horolovar 400-Day Clock Repair Guide, which is now in its ninth edition with accumulated sales of over 60,000 copies.
Today Mr. Terwilliger operates The Horolovar Company, largest supplier in the world of various repair aids for 400-Day Clock repairmen, and Clock Trade Enterprises, a subsidiary company, involved with other horological activities, including publishing and distributing horological books.
Mr. Terwilliger has been an active member of the National Association of Watch and Clock Collectors for many years and has served as an officer of the Association and as chairman of several of its national committees. He is currently a member of the editorial committee of the Association's Bulletin, and a trustee of the NAWCC Museum in Columbia, Pennsylvania. For many years, he has been a member of several horological societies in the United States and Europe.