The common unit of pressure employed in the field of oceanography is the decibar (abbreviated db). This is defined by
Standard atmospheric pressure at sea level is approximately 10 decibars.
The decibar is a convenient unit since a change of pressure of 1 decibar is sea water is associated with a change of depth of approximately 1 meter, which in turn is approximately equivalent to a change of dynamic depth of approximately 1 dynamic meter. Actually, under hydrostatic conditions
in CGS units. However, if p is expressed in decibars, in dynamic meters, z in meters, in gms/ , and g in m/ , then
But, since is only slightly greater than 1 gm/ (1.02 < < 1.08 gm/ for the ocean as a whole) and since g/10 is only abouta 2 per cent less than 1 m/ , the approximate equality of the numerical value of dp, and dz in Eq. (24) is evident.