MMP.18:4.1 - Identify what the models share and what they exchange

Start from the required result and trace which component supplies each quantity it uses. Recover the quantity’s referent, unit and reference point, as well as any time interval, spatial region or probability conditioning that changes its meaning.

Distinguish a shared quantity from a transferred result. If both models describe the same unknown offset, retain one common offset or a justified relation between their coordinates. If one supplies an estimated offset to the other, specify whether the receiving calculation uses its uncertainty or only an approximation by a point value.

Locate overlapping subject effects. If both component laws already include the same interaction, composing them may count it twice. Decide from the subject model which contribution is being retained and which is a second description of it. A.3.3.TR and C.29.BB supply the resulting joint change and balance relations.

Also recover the operating conditions. A component calibrated for one boundary condition may cease to apply when connected to a responsive neighbor. Replacing a supplied input by another model’s output can therefore require a changed component law, even when the variable types match.