The Dichotomous Key...

Is the cell diameter between 1.4 and 1.6 micron and is heavy attached growth observed usually ( 1 ) or is the cell diameter <= 1.0 micron ( 2 ) ...?

Both the average diameter and its range in micron should be measured; it is important to note whether the diameter is greater than 1 micron or less than 1 micron.