Atmospheric pressure measurements are unique among the meteorological variables that can be measured at a single site on the surface of Mars, providing the widest ranging study of phenomena and of space and time scales. Atmospheric pressure on Mars is approximately<B> 1%</B> of that on Earth and varies about plus/minus <B>15%</B> during the year due to condensation and sublimation of its primarily <B>CO<SUB>2</SUB></B> atmosphere on to and from its polar caps. Spatial processes from "dust devil" size structures, to "fronts" to regional and global dust storms, have been investigated from orbit, while temporal variations from the transient dust devils, to fronts, to seasonal and the dramatic year to year presence or absence of the global storms, have been studied by these single point, long term, Viking observations. The Viking Lander observations provided the first and most complete description of the weather at the surface of Mars, and the <A HREF="http://www-k12.atmos.washington.edu/k12/resources/mars_data-information/mars_overview.html"> <B><I> only Martian meteorology station Climate Record; </I></B></A> this is described in the Mars component of <A HREF="http://www-k12.atmos.washington.edu/k12/"> <B><I> Live from Earth and Mars </I></B></A>.