C.16.IR:4.1 - Fix the sought distinction and available relation

State the quantity or property being sought, its subject and conditions, and the question that depends on it. Distinguish the state before measurement, the state during interaction and the reported indication when they differ. For the voltmeter case in :5.1, the target is open-circuit source voltage, while the reading is the voltage with the instrument connected.

Recover the relation used to interpret the indication, including the domain of each unknown, relevant calibration, influences and error assumptions. Keep a known input as known and an unknown influence as a variable. Derive a missing contribution with C.16.MR before treating it as part of the available relation.

A domain restriction needs its subject meaning. Positive length, a known rotation range and a passive resistance bound can exclude mathematical solutions when those conditions hold. An inconvenient branch is a reason to inspect the model, not a reason to drop that branch.

State whether the receiving question needs a point value, an interval, a threshold decision or a comparison. This selects which remaining differences matter.