Tried an experiment this week comparing "resting" poly crosses between pulls and not. Background: some believe that one should allow polyester strings to "rest" between pull and clamping off. IIRC this might be part of the "JET" method. In any case, the idea is to increase the lifespan and playability of the polyester and manage tension loss. This week I had two matched frames strung the same way on the same type of machine. Stringer A allows a poly to rest as described above. Stringer B does not. The results were absolutely clear: the frame strung by A, with the poly crosses allowed to rest, provided more "pop" but less control and far less spin. Over time one can even see the poly crosses almost "sag" in an odd way as they are not perfectly straight in the bottom of the head. The distance is very tiny but clearly visible. The frame strung by B, with no rest between pull and clamp off, provides far more spin and control if less pop/power (which I prefer). And the crosses remain perfectly straight after an equal period of play (one match each with some serve and wall practice too). The difference was most noticeable on flat serves. The "rested" frame strung by A made it more difficult to keep my flat serves down. Too many sailed long. The frame strung by B generated enough spin even on flat serves to pull the ball down and in with plenty of pace. It was a joy to serve with B while A was just a headache. Same thing on ground strokes. A tended to sail closer to the baseline or over while B provided a more spin and a heavier shot. Lesson: at least in gut/poly hybrids, mushy crosses provide less spin and control compared to tighter crosses. I suppose this is one reason poly crosses work so well with gut mains but the lesson here is that even a poly cross can be too mushy to do its job of providing solid, stable support for the gut mains.