Correctly choosing a proper replacement main spring when a clock has missing springs (or the wrong springs installed) is a very common problem that clock repairmen often face. From the beginning of his career as a clock repairman, Richard Hansen noticed that when his customers brought him their clocks to be repaired, he would often see evidence of poor repairs, poor techniques and even gross mistakes inflicted on them by previous repairmen. He wondered why he should believe that every spring he found was, in fact, the perfect one for the clock in question? And when he found a spring where the outer end had obviously been re-worked (thus making the spring a bit shorter), he wondered how he would know if it was not then too short? Was it possible to redo the end again, or will that make the spring impossibly too short then? This book is a result of his work to answer some of those questions about choosing springs. It provides a methodology whereby answers can be found by using a set of look-up tables. It's a solution intended for the use of clock repairmen at their bench to find those answers with a minimum of time and effort needed for any given clock in front of them.