Thank you, but i just want to add this field from the UI

I don't have much experience on the UI part. What you are saying may not be possible, as you are accessing a field from another module that does not depend on the previous field module (if that makes any sense: you are binding 'mrp' to 'sales', even tho it was not designed this way).
Hope someone can clarify you if that can work or not.

PD: You can try creating a module using studio, and make the field there, and then just create the views... Not sure if that would work either.