machine if gear 94 has one hundred twenty teeth hall effect sensor 92 will generate one hundred twenty pulses for each needle stitch as best seen in fig1 beam revolution detector 80 includes permanent magnet 84 embedded in worm wheel 106 and hall effect sensor 82 mounted adjacent worm wheel 106 such that as beam 14 rotates magnet 84 passes by sensor 82 with each such occurrence hall effect sensor 82 generates a pulse which is received by computer 20 each pulse thereby corresponds to a single complete revolution of beam 14 in this way computer 20 is able to monitor and count the number of revolutions of beam 14 over a given period of time and compare the count with a given set point as best seen in fig1 and 2 control device 60 includes case 62 which houses torque motor 64 drive gear 66 motor shaft 68 and driven gear 70 case 62 includes tubular housing 67 which is adapted to receive spindle housing 109 housing 109 is secured within housing 67 by means of key slot 75 and threaded bore 74 each of which are formed in housing 67 and key stock 74b and set screw 74a more particularly set screw 74a is tightened down thereby driving key stock 74b into frictional engagement with the outer surface of housing 109 preferably an identical arrangement not shown is provided at a position on housing 67 radially offset from that shown in fig2 by 90 u00b0 spindle 108.