al axes the most commonly used of these include include bar, millibar, decibar, and atmosphere (atm).</li>
<li>units of length as listed in the file udunits.dat. For vertical axes the most commonly used of these include meter (metre, m), centimeter (cm), decimeter (dm), and feet (ft).</li>
<li>the (dimensionless) units "level", "layer", or "sigma_level"</li>
<li>other units listed in the file udunits.dat that may under certain circumstances reference vertical position such as units of density or temperature