I used LM324N(4 opamps on 1 chip) from ON semiconductor to build an Instrumentation Amplifier circuit. I chose the values of the resistors so as to give a gain of 640. But when i checked the gain on the CRO the gain was around 175. What problem could this be? Datasheet link:http://www.onsemi.com/pub_link/Collateral/LM324-D.PDF"