Read the start and the slide separately
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The first peak on a film friction trace is the force needed to start motion under the test conditions. The force measured over a specified interval once the sled is sliding describes a different part of the trace. Divide each by the normal force when reporting the corresponding coefficient. A large drop can indicate that the first movement needs more force than continued travel. A single drop at startup does not establish a repeating stick-slip pattern or identify the cause.
Compare the whole trace under matched conditions
Suppose two overwrap films slide with similar force after startup, but one has a higher peak. A line that repeatedly stops and restarts might respond differently to the two films even if their sliding averages look alike. For a fair comparison, match the contacting faces, sled load, pull speed, waiting time and conditioning. Retain the traces so a short spike, a broad peak and repeated oscillations remain visible.
A laboratory sled measures one defined contact. If feeding or unwinding is the decision, try the candidate film on representative guides and at the intended operating conditions.
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