One of his first instruments, created in 1932, was the Benioff seismograph, which senses the movement of the earth – these instruments are now used in every country in the world. Equally famous is the Benioff strain instrument, which records the stretching of the Earth's surface. One of his most recent accomplishments was a refined version of the old Benioff seismometer which has given seismologists more knowledge about the cause of very deep earthquakes.