BIOMERIDIAN BEST Galvanic skin response tester model# MSA-21 used in electrodermal screening measures electrical resistance and polarization at acupuncture points and meridians BIOMERIDIANS BEST MSA-21 Bio-energetic stress testing. unit is pre-owned with battery charger Included. unit is untested without the power cord, selling for parts or not working. but in good condition to fix or for parts.