Columbia subject headings:
Electromechanical devices.
Optical instruments.
Harvard subject headings:
Electromechanical devices--Congresses
Electrooptical devices--Congresses.
Optical instruments--Design and construction--Congresses
Princeton subject headings:
Electromechanical devices--Congresses.
Electrooptical devices--Congresses.
Optical instruments--Design and construction--Congresses.