English: Photos of pocketwatch mainsprings made by Elgin Watch Co. around 1910, from a service bulletin published by the company. Shows three types (l-r): normal, semi-reverse, reverse. The reverse curves given to the outer portion of the spring in the last two types provided additional torque during the later part of the watch's running period as the spring was running down. This produced a more constant drive force for the watch movement, resulting in greater accuracy. Alterations: cropped out frames and captions, combined 3 separate photos, cloned background of 2nd photo to cover blank areas of composite, converted to PNG