[pcubis]

Question 1:
When I'm measuring redox with a calomel reference probe, platinum wire, and a voltmeter, do I record the numbers as is (+ or -) and then make the corrections? 

I was confused because one of my classmates told me the values we measure out in the field should all be negative.  I have been getting more negative values from the voltmeter than positive, but according to my friend, I needed to change any positive readings to negatives and then plugged that value into the equation below:

EhSystem = EhObserved + EhReferenceStandard -   
                 EhReferenceObserved + EhFieldCorrection
Example values respectively:         
 183   177   240   -28
which yield "EhSystem" = 218

Question 2:
For a sulfate reducing condition, what is the approximate mV range? 

Thank you in advance.