The mainspring is the mechanical watch’s main source of power. The mainspring is a coiled piece of spring that when uncoiled will cause trouble in the motion works. This can diminish the remaining time the watch can run. The technical term for the amount of time the watch can run is called the power reserve. The power reserve is somewhat similar to a fuel gauge of a car since there is an indicator in the dial. Usually, it is being shown in the dial in a form of an angle or a linear indicator.
A differential screw is what is being used in a power reserve complication. This is a wheel that is being screwed into the shaft parallel to the barrel. The top of the differential screw has a tapered section that will direct the power reserve indicator hand as it moves up and down the threaded shaft. This is done through establishing a link having a finger on the section that was tapered.
The differential screw will descend to the threaded shaft as a result f the barrel’s movement when the watch is running. The taper’s angle will fit with the differential screw’s sequential turns for the power reserve indicator to adjust. To guarantee that the differential screw is accordingly coinciding with the barrel’s teeth, its teeth must be thick enough to accommodate the desired torque load.
The threaded shaft has an attached wheel that when the watch is being wound will also be driven. When this threaded shaft is driven this will result to an ascending movement of the power reserve indicator hand and will position it in its actual available power.
There are as some more advanced mechanical watches that have an upgraded version of the power reserve complication. This version includes an epicyclic and differential system. Both of these systems indicate power reserve in a linear rather than angled formation. With regards to the latest craze in the watch making industry, which is the skeletonized watch, they are built in with a “natural” power reserve indication. The barrel and its cover are eliminated so that the unwinding of the mainspring is visible.