Sum of (ROC of security ABC - ROC of security XYZ)

[Jim Harmon <jrh@xxxxxxxxxxxx>]

I need make an indicator (or Expert) that calculates a sum of the
difference between the same formula applied to two *different*
securities.

For example, Sum of (ROC of security ABC - ROC of security XYZ).

Is there any way to do this in MS? How would I do this if the formula
applied to the securities (ROC in the above example) is a custom
indicator I need to design?

Thanks very much!

Jim Harmon