This timer is useful for students to develop basic understanding of constant speed, acceleration and deacceleration. It operates on 12V a.c. and is therefore quite safe for work by studei";s in the dynamics lab. This timer has an electromagnet with spring loaded, striker which strikes the paper tape drawn through guides. It is supplied along with a tape roll and carbon discs. Dots are spaced at 1/50 or 1/60 second intervals depending on a mains frequency. With stand for tape but without tape.