axis and stats. 
Note that strings are assembled here without accessing to <cite>dataIO.arrays.stats</cite> function, whose <cite>fmt</cite> argument is not used at all here.</p>
<p><cite>units</cite> are used and appended to <cite>fmt</cite> if not None or set to empty string.
The length of the two must match, and are converted to the correct format inside this function.
Conversion is made in this case in dependance on the format of <cite>vars</cite>. For example, <cite>vars = [[1,2,3],None,None]</cite> re