Roller-Jewel—Same as "impulse pin."
Roman Indiction—A period of fifteen years appointed by the Emperor Constantine 312 A. D. for the payment of certain taxes.
Rose Engine—A lathe in which the rotary movement of the mandrel is combined with a lateral, reciprocating movement of the tool rest; used for ornamenting the outside cases of watches with involved curved engraving.
Ruby Pin—The impulse pin in a lever escapement, made of a ruby.
Ruby Roller—The roller in a duplex escapement against which the teeth of the escape wheel are locked.
Run—In the lever escapement, the extent of the movement of the lever toward the banking pins after the "drop" on to the locking.
Sabinianus—Pope from 604 to 606. Said to have invented a clock in 612 A. D., but the clock he is supposed to have built was probably only another of many forms of clepsydrae, or water clocks.
Safety Pinion—A center pinion in a going-barrel watch which allows the recoil of the barrel if the mainspring breaks.