[P7.2]
is: the pressure due to the weight of the atmosphere. [P7.2]
is not: a constant, but varies with time and position. [P7.2]
has a value: at the Earth's surface varying only by relatively small amounts. [P7.2]
has as a useful unit: the standard atmosphere (see atmosphere, atm) defined by [P7.2]
Copyright 1997, The Open University