How to measure distance between shells in eQuest?

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I have two shells in eQuest, separated by an unknown distance. I'd like to measure the distance between the shells so I can position them as needed. The position doesn't really matter for the simulation itself, it's more for it to "look" better. I need to know how to measure the distance between the two parallel walls (or between the roof of one shell and "floor" of a shell above). Is there a way to measure htis? I would then go into the shell and adjust its position on Screen 1 in the wizard ("Specify Exact Site Coordinates"). Thanks!