waterproof housing the pacing device 20 is deactivated when the shaft 34 is positioned in its counterclockwise most position by rotating the shaft 34 in a clockwise direction the astable multivibrator circuit is activated and current is intermittently applied to the led 22 the led 22 is rhythmically activated in response to the current thereby conveying a metronome like visual signal the frequency of the led 39 s on off cycle is controlled by the position of the shaft 34 and is increased as the shaft 34 is rotated in a clockwise direction by actuating the shaft 34 the swimmer may adjust the pacing device to convey a pacing signal of the preferred frequency the presently anticipated range of adjustment is 30 to 120 cycles per minute cpm as shown in fig4 the invention is driven by a potentiometer controlled astable multivibrator circuit these circuits are well known to those having skill in the art in a preferred embodiment the astable multivibrator circuit includes a 555 integrated circuit 46 the output of the 555 integrated circuit 46 oscillates between a high approximately source voltage level and low state approximately ground level as is well known the frequency of this oscillation is a function of the resistance and capacitance along various points within the circuit the potentiometer 44 provides a means to vary this resistance and thereby vary the frequency of the oscillation the invention has been described in conjunction with swim goggles but is equally applicable to any activity in which a pacing or other periodic signal is desirable such activities might include running bicycling or aerobics the above description is that of a preferred embodiment of the.