This is a 100% mechanical working clock, which means it runs off of no electricity or batteries. Instead it is powered by a weight falling slowly over time, which is attached to a string that pulls on a spool, creating the spinning motion that powers the clock. The speed of the clock is regulated by an escapement wheel and pendulum, which converts the energy into even increments of time, and is what generates the "tic, toc" noise a clock makes. Adjusting the length of the pendulum adjusts the speed at which it tics, which is why i built an adjustable pendulum using Technic worm drives, which is why my clock is able to be accurate up to a few seconds for every hour. The gears spinning the escapement wheel, also power the minute hour and second hands of the clock, which display the time on the front, with each little circle on the outside ring representing 1 hour, or 5 minutes. The for every one rotation of the hour hand, the minute hand revolves 12 times, and for every 1 revolutions of the minute hand, the second hand revolves once. These ratios are achieved using gear ratios which alter the speed at which different axles spin. The clock will run for over an hour, for every 3 feet the weight falls, however the clock uses special differential gearing to allow it to be wound while it is still running, meaning the clock never has to stop. The winder is located on the "2" hour spot on the face of the clock. If the clock isn't winded, and it stops ticking, the time can easily be set by the adjustable minute, hour, and second hands. The second and hour hands can be adjusted without moving anything else, but adjusting the minute hand will result in the hour hand also adjusting, to ensure it is in the proper position. The clock is made entirely from Lego pieces, except for the string and weight. However, i don't anticipate this becoming a problem because many other sets come with string, and the weight is extremely easy to make at home. (Mine is just a soda can full of pennies). One of the best things about the clock is that there is no adjusting required, if assembled properly it will work fine. This is a lot of information, which is why I included a few diagrams with the pictures. A video can be found on Youtube under "TheRedEcho", or "Eric Mass".