Why an unbroken string is not necessarily a good string for longer

Try these steps in order

1. Immediately after installing a fresh string, record the date, material, gauge, reference tension, and stringer, then keep the first session's sound, impact feel, and average trajectory as a baseline. Note that the machine-set reference tension is not the same as the strings' current actual tension. Add playing time in 30-minute increments and finish each session with one line such as “depth consistent,” “ball suddenly launches,” “mains no longer snap back,” or “fraying spreads.” Do not record only the break date.
2. Designate a 10-ball service-box rally and a 20-ball baseline crosscourt rally as regular inspection drills. If the same depth now requires less force or a more closed racquet face than usual, record that you may be compensating for a response change. Photograph the center intersections from the same angle: observe notching and snapback for polyester, fiber wear for multifilament, and coating and fraying for natural gut. Keep visible wear and on-court response in separate columns because they need not change together.
3. Define the replacement criteria you will accept in advance. For example, if trajectory inconsistency appears in two consecutive sessions, or impact-feel change and reduced snapback occur together, consider useful life over even before breakage. Compare candidates by dividing total installed cost by satisfactory hours. Use the cost of maintaining a reproducible condition rather than the cost of leaving a cheap string installed for a long time; if costs are similar, choose one that is easy to source, restring, and track.