Tests whether a 'units' object is actually
unitless.
Unitless objects, such as ratios, should be assigned
units of '[1]'. Often they are, but
sometimes unitless ratios are assigned units like '[m/m]'.
The units
package should always convert '[m/m]' to
'[1]', but it does not always.
Sometimes units like '[m/m]' mess things up, so it is
better to remove them before calculations.