Clocks are available in a wide range of different styles and sizes, with many variations on the classic analog design and a number of new modern digital time keeping devices. There are a number of factors which influence how individual clocks (Standuhr) are made, including the type of time display and the method that is used for time keeping. The vast majority of time keeping devices can be categorised as either analog or digital, with analog designs using angles to indicate time. In contrast, digital clocks generally use a numeric display to indicate time, through either a 12 or 24 hour display. However, it is important to note that the type of display is not always a good indicator of the technology inside, with some analog displays using digital time keeping technology instead of a traditional mechanical construction. Clocks are made according to their display mechanism and their method of time keeping.
The invention of the modern clock took place in the 13th century, with time keeping devices before this time looking very different to those of today. Before the 13th century, people measure time through two primary means, water clocks and sundials. However, due to advances in accurate mechanical time keeping technology in the 13th century, people around the world finally had the ability to own and utilise accurate personal time keeping devices. The methods used in mechanical clocks vary according to their construction, although all oscillating clocks, whether analog, digital, or atomic, share a number of similarities. In all cases, a precisely tuned oscillator keeps a beat through the act of repetition, with a controller device used to sustain the oscillators motion and replace any energy that is lost due to friction.
Along with the type of display and the method of time keeping that is used, there are also considerations in terms of the final form of a clock. Clocks can vary a lot in both size and construction, with some common modern materials including plastics and metal. No analysis of clocks can take place without a look into digital time keeping devices, as they have become the primary means that most people tell the time in the 21st century. Most digital clocks use an LCD, LED, or VFD display to indicate the time, and various power mechanisms that are connected to a battery of AC power line.