The rowland telegraphic system

Louis M. Potts
1907 Proceedings of the American Institute of Electrical Engineers  
The normal operating speed is fixed at 210 revolutions of the line unit per minute, or three and one-half revolutions per second, or one revolution in one divided by three and one-half, or two-sevenths of a second. This interval of two-sevenths of a second being divided among four operators, gives each one the use of the wire for two sevenths divided by four, or one-fourteenth of a second.
doi:10.1109/paiee.1907.6741641 fatcat:cmsqysrxvbhythmh6wud3g6mxq