You are going to need to get yourself a Digital Multi Meter..
You can get them for around $10.00. It will be a good
investment.. :'( They even have them on eBay.
Your meter's lowest scale is 2.5VDC. and it has an Analog
display. You will have problems reading 1mV or even 10mV
variations. :-/
IMHO... get yourself another meter and come back here and
we will show you how to use it.