Cylindrical coordinates are often given as so that is azimuthal in the same sense as spherical polar, and so that is differentiated from . However, many other similar conventions are used. For example, or or are not uncommon. We will use in this review to avoid as much confusion as possible with spherical polar coordinates.
But Note Well: is now a function of ! Similarly:
with a function of the angle that defines the direction of . Specifically:
And again, there are many other possible 's, for example:
for an end cap of a cylindrical volume.
for the second of these area elements.