PHY.9:4.4 - Include the effect of measuring on the subject

Construct the coupled subject-probe account for the duration that matters. Determine whether connecting the probe changes the sought quantity, changes only another quantity, or leaves its relevant value effectively unchanged. Use the physical coupling rather than a universal claim that measurement must disturb the target.

If the wanted value precedes coupling, derive how it can be recovered from the disturbed response, or change the arrangement to reduce the consequential disturbance. Keep uncertainty in that recovery. When correction is poorly determined, a different interaction or a conditional range can be more useful than more decimal places.

Compare the retained effect with the allowed error or decision margin. Loading, finite response time and backaction matter through their consequences for this question. PHY.5 helps justify an approximation. A usable result does not require modeling every interaction.

A nondestructive or non-demolition measurement protects a specified property under particular conditions; it does not establish that every later use of the subject is unaffected. Preserve any disturbance that changes the receiving experiment or work.