locked following phase at least on average referring now to the block diagram portion of fig1 a master clock 30 is composed of a crystal pulse generator such pulse generators are very commonly used for timing devices such for example as precision instruments electric wristwatches are a common example the crystal in the clock 30 has an output frequency far greater than the frequency needed for the purposes of this invention and therefore a frequency divider is used to reduce the frequency into a useful range a dotted outline component 32 is placed in the diagram on fig1 to indicate the use of suitable frequency divider circuitry in the event a high frequency master clock srystal is employed with a range higher than useful if a master clock of lower frequency is available then it is not necessary to use a divider 32 when a proper range frequency is established by means of the clock 30 and possibly a divider 32 that frequency is directed to a counter 34 counter 34 is programmable by a program register 36 in the context of photocomposition it is presumed that the programmable register 36 will be employed under the control of the master controller and software for the photocomposition machine because it will be necessary to change the number in the counter 34 according to the dictates of the text being composed the control register 36 exerts its control influence upon the counter 34.