Apparatus for transcutaneous electrical nerve stimulation in a user, the apparatus comprising:stimulation means for electrically stimulating at least one nerve；an electrode array connectable to said stimulation means, said electrode array comprising a plurality of electrodes for electrical stimulation of the at least one nerve, said electrodes having a pre-formed geometry and known electrode-skin contact area size when in complete contact with the user's skin；monitoring means electrically connected to said stimulation means for monitoring the impedance of the electrical stimulation through said electrode array； andanalysis means for analyzing said impedance to estimate a change in the electrode-skin contact area.
