I don't understand how your figures relate to each other in the example you
gave, but here are a few ways to format a float to one decimal place:

  val = 0.4423

  printf "%6.1f mcg\n", val

  str = sprintf("%6.1f mcg", val)
  puts str

  str = "%6.1f mcg" % val
  puts str

For more info: ri Kernel#sprintf, ri String#%