The Doppler effect (or Doppler shift), named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague, is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.

"In the land of the blind, the one-eyed man is king." - Desiderius Erasmus

Reserve Deputy Probation Officers are deputized volunteers who have received special training in order to assist Probation staff in a wide range of supervised responsibilities, that include direct involvement with juvenile an d adult probationers. Reserve Deputies are highly motivated, skilled, and caring people who want to serve their community as a part of the Los Angeles County Probation Department. Reserve Deputies are not a replacement for or an alternative to paid staff, but are intended to be an enhancement to existing resources.

Deadweight tonnage is a measure of how much weight a ship is carrying or can safely carry. It is the sum of the weights of cargo, fuel, fresh water, ballast water, provisions, passengers, and crew.

An oil tanker, also known as a petroleum tanker, is a merchant ship designed for the bulk transport of oil. There are two basic types of oil tankers: the crude tanker and the product tanker. Crude tankers move large quantities of unrefined crude oil from its point of extraction to refineries. Product tankers, generally much smaller, are designed to move petrochemicals from refineries to points near consuming markets.