Ron, about 45 years back I built a comparator circuit which is an audio 
oscillator Which you use in parallel with an existing meter. You turn the 
pot to the direction you want to point your beam and flip a switch,  when 
the meter side of the switch tone matches the tone of your pointer, your 
there.  I think the circuit came from the Braille Technical Press.  I still 
use it today.  Ed K7UC