Not sure I follow you. Please correct me if I’m wrong, but I would assume first of all that what’s involved in making the balance, among other mechanical considerations, is using different equations from relevant theories to figure out how to put the circuits together in the balance in such a way as to give the correct measurement of whatever is being measured.
But the balance giving the correct measurement doesn’t depend on the theories explanation. It depends on working out the theories equations correctly and putting the circuits together correctly to get the correct results when measuring an object. And assuming the equations have been confirmed to work would make them an objective aspect of the production process.
Sure, knowing about the theories is needed by those working out the equations so they know which equations to use, but that’s the only aspect I can see where the theories would play a role. As long as the equations used are confirmed there’s nothing I can see that would be subjective about the measurement. The explanation of why the balance gives the correct measurement may be subjective, but not the actual measurement. Does that make sense?
Also, I notice the conversation seems to have shifted a little from direct/indirect back again to objective/subjective. They’re both relevant, but just wanted to point that out to avoid confusion.