Countdown timer history

The first countdown timer were (if it can be called so) sundials which the shadow of the pin, which moves as a result of the rotation of the earth, a measure for the time indicated. Through hourglasses and various other mechanisms eventually became the mechanical pendulum  timer. From that moment the time with any accuracy. The invention of the mechanical  timer is attributed to the Frenchman Gerbert (later Pope Sylvester II), who lived around the 10th century. Until the early modern period was a  timer the most complicated machine that one could make.

At sea, a pendulum  timer unusable. Only after the invention of the unrest could also be measured accurately as the time which the accuracy of the navigation benefited. The sun's position is indeed together with the time and position at sea.

 timers with a sling and with a restlessness in comparable accuracy. A deviation of one minute per week is possible.

Even more accurately, the use of a quartz crystal, the operation of which is based on piezo electricity, deformation as a result of an electric voltage and vice versa. A deviation of less than 1 second per week for a quartz movement feasible.

The most accurate  timers are atomic  timers, which are directly on the definition of the second based.

Besides the sundial, there are also modern  timers that keep time from an external source involved: eg radio  timers.
Time Display
Arabic dial with 3 groups pointers
File :22-digital- timer screencast. Ogg
digital  timer principle

We can also distinguish  timers to the method of time display:
An analog  timer typically has a dial 2 or 3 and driven by the  timer hands, fixed to concentric shafts which pass through the center of the dial stabbing.

The rest of the mechanism is then situated behind the dial. The order in which the pointers are, is almost always the same. The only exception is the wekwijzer that is at or below the hour hand can be located and then in a different way functions. The wekwijzer is therefore discussed separately below.

    The second hand is on top. This is usually a long, thin needle, sometimes of a different color to avoid confusion with the other hands to avoid.

There are also  timers with a short second hand on a separate, small needle plate. Older  timers often have no second hand. The second hand makes one revolution per minute (60 seconds) and sometimes the numbers 0 t / m 59 (or only the multiples of 5) along the perimeter of the dial indicated. In general, the second hand does not put the same: it is possible that the countdown minute timer hand exactly one minute while the second hand is not pointing upwards.

    Under the second hand is the minute hand, also called big hand. This is thicker than the second hand. The minute hand rotates in one hour (60 minutes) around. Are the numbers 0 / to 59 along the circumference of the dial, then apply also to the minute hand. A  timer can often be put right by manually pushing the minute hand forward. The hour hand will then drop even further, the second hand does not.

    Among the minute hand is the hour hand and minute hand. This is shorter than the minute hand and often decorated. He makes one revolution per 12 hours. While the numbers 0 t / m 59 (for the minute hand and second hand) usually lacking, are usually the numbers from 1 t / m 12 along the circumference and sometimes also the numbers of 13 t / m 23. The numbers can also dashes or other symbols. The oldest  timers have only an hour hand, because they are not very accurate and previously little one was interested in an accurate time indication.