message: no need for config's tip length when user attach unknown tip
diff: @@ -16,7 +16,7 @@ Z_PROBE_CLEARANCE_MM = 5.0
  BOUNCE_DISTANCE_MM = 5.0
  XY_CLEARANCE = 7.5
  -Z_CROSSOVER_CLEARANCE = 80 # How much of z height to be added to nozzle to clear the top
  +Z_CROSSOVER_CLEARANCE = 80 # Z mm between nozzle and probe
  def calibrate_container_with_delta(
  @@ -57,8 +57,6 @@ def probe_instrument(instrument, robot) -> Point:
  ('z', 0.0, Z_SWITCH_OFFSET_MM, rel_z_start, -Z_CROSSOVER_CLEARANCE) # NOQA
  ]
  - tip_length = robot.config.tip_length[instrument.mount][instrument.type]
  -
  acc = []
  res = {
  @@ -143,13 +141,12 @@ def update_instrument_config(instrument, measured_center) -> (Point, float):
  def move_instrument_for_probing_prep(instrument, robot):
  - tip_length = robot.config.tip_length[instrument.mount][instrument.type]
  # TODO(artyom, ben 20171026): calculate from robot dimensions
  robot.poses = instrument._move(
  robot.poses,
  x=191.5,
  y=75.0,
  - z=128 + tip_length
  + z=128
  )
  