HeroesofHorology.com

Horolovar 400 Day Clock

Repair Guide

Horolovar 400 Day Clock Repair Guide, 10th Edition, written by the late Charles Terwilliger, and edited by H.W. Ellison.
Copyright 1991, Hardcover, 237 pages.
ISBN: 0-916316-04-1

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The 10th edition is the latest. Known in horological circles as the bible of anniversary clocks, this comprehensive book is a must-have reference for serious collectors, horologists, and anyone with an interest in these beautiful timepieces. Features include:

  • The history of 400 day anniversary clocks
  • Patent information
  • Hundreds of photos of clocks and pendulums
  • A study of escapements
  • Troubleshooting and repair tips
  • Back plate illustrations
  • 400 day anniversary clock trivia
  • and more …

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Known errors and suggested updates to the 400-Day Clock Repair Guide from the NAWCC forum.

Charles O Terwilliger, Jr.

Charles Terwilliger’s contribution to horology can best be described as innovative and colorful. Not only did he revolutionize the accuracy of the 400-Day Clock, his research and clock reproductions continue to impact the world of clock collecting to this day.

HeroesofHorology.com was established in 2025 to honor the memory of Charles O Terwilliger, Jr and the company he established, Horolovar, and to fulfill the dream of his son, Robert Terwilliger, who wished for this biography to continue on after he himself passed away.