A microvolt (µV or mcV or uV) is a unit of measure of electric potential equal to one millionth (10-6) of a volt.
After Lieutenant Natasha Yar was attacked by Armus on the planet Vagra II on Stardate 41601 in the year 2364, Doctor Beverly Crusher used direct reticular stimulation to try to revive her. The charge was increased to 70, 85 and finally 90 microvolts before Dr. Crusher declared Yar deceased. (TNG: "Skin of Evil")