turns on those led 39 s 24 29 corresponding to the measured voltage as is evident from table i the battery analyzer 10 must be capable of resolving very small voltage differences for example a voltage difference of only 0 06 volts separates the voltage levels 12 42 volts and 12 48 volts that indicate respective charge levels of 65 and 75 moreover voltage changes in mid range are the most critical to insure accurate voltage measurement particularly in mid range the battery analyzer 10 employs a reference voltage feedback circuit which insures that the reference voltage at the center of the resistor divider 36 is correct to this end a feedback resistor r1 is connected from the center of the divider 36 to the inverting input 35a of the amplifier 35 this terminal also is connected to ground via a pair of resistors r2 and r3 the fixed reference voltage from the potentiometer 34 is applied to the non inverting input 35b of the amplifier 35 with this arrangement if the voltage at the center of the divider 36 should vary feedback via the resistor r1 and the amplifier 35 will cause an appropriate correction in the output voltage supplied to the divider 36 via the line.