electro-chronograph

from The Century Dictionary.

• noun A chronograph on which the record is made by electrical means: much used in astronomical observatories and in the laboratory for noting the precise instant or duration of transits and similar phenomena. See chronograph.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Astron. Physics) An instrument for obtaining an accurate record of the time at which any observed phenomenon occurs, or of its duration. It has an electro-magnetic register connected with a clock. See chronograph.