message: Take difference of offsets saved
diff: @@ -203,9 +203,11 @@ def save_new_offsets(labware_hash, delta):
  calibration_path = CONFIG['labware_calibration_offsets_dir_v4']
  if not calibration_path.exists():
  calibration_path.mkdir(parents=True, exist_ok=True)
  + old_delta = _look_up_offsets(labware_hash)
  + new_delta = old_delta + Point(x=delta[0], y=delta[1], z=delta[2])
  labware_offset_path = calibration_path/'{}.json'.format(labware_hash)
  calibration_data = new_labware._helper_offset_data_format(
  - str(labware_offset_path), delta)
  + str(labware_offset_path), new_delta)
  with labware_offset_path.open('w') as f:
  json.dump(calibration_data, f)
  