is divided by 10 by divider circuit 206 and the resultant signal is applied to a synchronous rate multiplier 208 via conductor 209 the multiplier circuit 208 generates an output signal having a frequency that corresponds to that of the input on conductor 209 multiplied by one tenth the value of an input signal on cable 246 which represents the contents of the percents units dial 242 if for example the percents units dial were set to 5 binary 0101 then the output rate of synchronous rate multiplier 208 would be 5 divided by 10 or one half its input rate the output of the synchronous rate multipler 208 is applied to a selector circuit 210 via conductor 211 further the selector 210 has received an input signal from the percent tens dial 244 on cable 248 and another signal from an add 1 circuit 214 on cable 213 which represents the values of the percent tens dial increased by 1 when the output of the synchronous rate multiplier 208 on conductor 211 has a first value for example zero voltage the output of the selector 210 on cable 215 corresponds to the value of the signal on cable 213 when the output of synchronous rate multiplier 208 has a second value for example a positive voltage the output of the selector 210 on cable 215 corresponds to the value of the signal on cable 248 the value represented by the signals on cable 215 corresponds to the percentage value set up in dials 242 and 244 the selector 210 produces an output value equivalent to the value of the tens dial 244 or.