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