re: Doesn't quite make sense . . .
There should be no "large electric fields" to find, merely potential energy differences between these masses.
The potential "energy" difference is exactly what causes an electric field. It's really only a potential until you consider a charged particle within the potential.
The potential they'd be looking for is the electric potential (voltage) and it's the negative gradient of the voltage (first spatial derivative) which is the definition on an electric field.
Mathematically you can see the relation (and proof i'm not making this up) in eq #4 here:
http://scienceworld.wolfram.com/physics/ElectricField.html