 
 if draw_diagrams
   draw_strings = ->
-    for n, i in StringNumbers
+    for i in StringNumbers
       x = i * string_spacing + h_gutter
       ctx.beginPath()
       ctx.moveTo x, v_gutter + above_fretboard

    positions

  frets_per_string = do (strings=([] for __ in OpenStringNoteNumbers)) ->
    for position in positions
      strings[position.string - 1].push position
    strings

  compute_choices = (by_string) ->

      continue if fretted_strings[string_number]
      ctx.font = "#{closed_string_fontsize}pt Helvetica"
      ctx.fillStyle = 'black'
      ctx.fillText "x", h_gutter + string_number * string_spacing - 1, v_gutter + above_fretboard - 2.5

draw_intervals_from = (root_position, semitones, color) ->
  root_note_number = pitch_number_for_position(root_position)
