How to use parameters that are defined in one subsystem in another subsystem?

I have defined a parameter, Jm in one subsystem, i want to add this to another parameter defined in another subsystem and use the sum in a gain block in the latter subsystem.

Any ideas or suggestions, pls post

Thanks

[Kaustubha Govind]

Could you explain what you mean by defining parameters in a subsystem? Is 'Jm' really an output of the subsystem, or is it really the value of a dialog parameter that is defined in the subsystem's Mask Workspace?