def match_axis_label_suffix(str)
      best = [nil, nil]
      Unit.each do |unit|
        label_s = unit.label.to_s
        best = [label_s, unit] if suffix?(label_s, str) and (best.first.nil? or label_s.length > best.first.length)
      end
      best
    end
def match_axis_label_suffix(str)
      best = [nil, nil]
      Unit.each do |unit|
        label_s = unit.label.to_s
        best = [label_s, unit] if suffix?(label_s, str) and (best.first.nil? or label_s.length > best.first.length)
      end
      best
    end
Returns the axis label and Unit which match on the label suffix substring, or nil
 if no match. For example,
   match_axis_label_suffix(:millimeter)
 returns "meter" and the meter Unit.