How to read manufacturers' numerical scales

Anyone buying a rubber or a blade for the first time meets three or four figures on the spec sheet: speed 9.5, control 8, spin 9, hardness 47.5°. The grid is clean and suggests a standardised system, comparable between brands the way centimetres or grams are. It is not. It never has been.

The problem at source is simple. There is no international body fixing how the speed of a rubber is measured or what an 8 for control means. Each manufacturer has developed its own scale taking its own catalogue as the reference. A 10 for speed at Butterfly means “the fastest we make in this segment”; a 10 at Yasaka means the same thing, but referred to the Yasaka catalogue. Within each brand, a 9 is faster than a 7 with reasonable reliability. Crossing brands — saying that a 9.5 from one “equals” the 9.5 of another — has no basis.

To this is added that the scales for speed, control and spin are not physical measurements. They are qualitative estimates by the manufacturer, produced by its technical team, with its reference players, glued onto its blades. When the catalogue says “Spin 9”, what it is saying is “our team considers that this rubber generates a lot of spin relative to the rest of our range”. It is an internal claim, not a verifiable datum.

Sponge hardness is a case apart: here there is indeed a physical measurement obtained with a durometer. But there are at least three scales in use — ESN, DHS, Butterfly — which measure with different instruments and at different points in the manufacturing cycle. Values that coincide at first sight — 47.5° on one and on another — do not express the same perceived hardness. The detailed treatment of the three scales and how to navigate between them is addressed in 4.3; the master table of equivalences, in Annex A.

There is a further source of confusion the experienced player learns to detect: the scales are readjusted over time. When a brand launches a product faster than its entire previous catalogue, the speed values rise. A 9.5 from ten years ago may be an 8.5 today, not because the product has changed, but because the catalogue has raised its ceiling. The object is the same; the ruler is not.

Faced with this picture, three principles guide a useful reading of manufacturer figures.

First: the numbers of one brand serve only to compare products of that same brand. Internal comparison is reliable; cross-brand comparison is not.

Second: the speed and spin scales must be read together with the type of rubber. A 9 for spin on a tacky Chinese rubber means something different from a 9 on a European tensor: the first generates spin through the grip of the topsheet at low speed, the second through sponge compression at high speed. The number summarises without distinguishing, and the distinction matters when choosing.

Third: the control value is the least reliable of all, because the very concept of control — as discussed in 2.2 — depends on the player doing the evaluating. It is best taken as an indicative figure, not a guarantee.

Spec sheets are useful for ruling out manifestly unsuitable products — a rubber labelled with maximum speed and minimum control will hardly suit a beginner — but not for deciding between products that are reasonably close. The final decision goes through the feel of the rubber mounted on one's own bat, with one's own game. The numbers orient; they do not substitute. The criteria for taking that step are addressed in chapter 7.