• The cathodes (negative electrodes) could be placed at different distances from targeted nerves.
  • It could be that the supramaximal stimulating current was not first established for both stimulators independently.
  • It could be that one or more electrodes dried out.
  • It could be that the polarity of some electrodes was reversed.
  • It is a known fact that stimulation of the ulnar nerves on one patient’s two arms would results in different TOF ratios if all other setup factors are significantly similar.