Differential Analog Input Arduino Micro

I'm trying to read signals off a flow sensor. I usually use NI DAQ to read a differential analog voltage input. How do I do the same in Arduino Micro?

I tried the code here http://forum.arduino.cc/index.php?topic=147830.0 , but throws an error 'multiple definition of analogReference'.

Any help on how to go about this will be great. Thanks!

Copied the error message below:

sketch/DifferentialArduino.ino.cpp.o: In function analogReference': sketch/wiring_differential.c:38: multiple definition of analogReference'
sketch/wiring_differential.c.o:sketch/wiring_differential.c:38: first defined here
sketch/DifferentialArduino.ino.cpp.o: In function analogReference': sketch/wiring_differential.c:38: multiple definition of analog_reference'
sketch/wiring_differential.c.o:sketch/wiring_differential.c:38: first defined here
core/core.a(wiring_analog.c.o): In function analogReference': /Applications/Arduino.app/Contents/Java/hardware/arduino/avr/cores/arduino/wiring_analog.c:35: multiple definition of analogReference'
sketch/wiring_differential.c.o:sketch/wiring_differential.c:38: first defined here
core/core.a(wiring_analog.c.o): In function analogReference': /Applications/Arduino.app/Contents/Java/hardware/arduino/avr/cores/arduino/wiring_analog.c:35: multiple definition of analog_reference'
sketch/wiring_differential.c.o:sketch/wiring_differential.c:38: first defined here
collect2: error: ld returned 1 exit status
exit status 1
Error compiling.

Try yourself. Set registers to match your needs. See pages 314-> of datasheet