sensor - Studying Behavior of an EEG Device

I have an EEG brain signal measurement device. I need to calibrate it -- i.e., I need to be able to apply known voltages to it and see its output. After doing this many times, I want to be able to determine the relationship between an applied voltage at the terminals and the output it gives. Any ideas on how I could do this? Is there a particular device that I could use to apply the deterministic voltages? I understand the voltages read by such EEG devices are so low and hence susceptible to noise. Would this affect me so badly. I am from CS, no much knowledge on EE