Multimeters were invented in the early 1920s as radio receivers and other vacuum tube electronic devices became more common. The invention of the first multimeter is attributed to British Post Office engineer, Donald Macadie, who became dissatisfied with the need to carry many separate instruments required for maintenance of telecommunications circuits.Macadie invented an instrument which could measure amperes (amps), volts and ohms, so the multifunctional meter was then named Avometer. The meter comprised a moving coil meter, voltage and precision resistors, and switches and sockets to select the range.The Automatic Coil Winder and Electrical Equipment Company (ACWEECO), founded in 1923, was set up to manufacture the Avometer and a coil winding machine also designed and patented by MacAdie. Although a shareholder of ACWEECO, Mr MacAdie continued to work for the Post Office until his retirement in 1933.
A respirator is a device designed to protect the wearer from inhaling particulate matter, including airborne microorganisms, fumes, vapors and gases. There are two main categories: the air-purifying respirator which forces contaminated air through a filtering element, and the air-supplied respirator in which an alternate supply of fresh air is delivered. Within each category, different techniques are employed to reduce or eliminate noxious airborne contaminants.
The importance of traffic safety is obvious; traffic accounts for many deaths and injuries. According to the World Health Organization, road traffic injuries caused an estimated 1.26 million deaths worldwide in the year 2000. The average rate was 20.8 per 100,000 people, 30.8 for males, 11.0 for females . Measures can be taken in order to reduce the number of casualties and injuries greatly.