IT TOOK a leisurely 70 years after King Gillette invented the safety razor for someone to come up with the idea that twin blades might be—or, at least sell—better. Since then, the pace of change has accelerated, as blade after blade has been added to razors in an attempt to tech-up the “shaving experience”.

For the most cynical shavers, this evolution is mere marketing. Twin blades seemed plausible. Three were a bit unlikely. Four, ridiculous. And five seems beyond the pale. Few people, though, seem willing to bet that Gillette's five-bladed Fusion is the end of the road for razor-blade escalation. More blades may seem impossible for the moment—though strictly speaking the Fusion has six, because it has a single blade on its flip-side for tricky areas—but anyone of a gambling persuasion might want to examine the relationship between how many blades a razor has, and the date each new design was introduced.

This relationship (see chart) suggests shavers are going to get more blades whether they need them or not. However, just like Moore's law—the observation that computer chips double in power every 18 months or so—it seems that technology as well as marketing determines the rate at which new blades are introduced.

It is simply not possible to add a new blade whenever the marketing department wants one. Every additional blade, explains Michele Szynal, a spokeswoman at Gillette, adds weight and size to a razor. Firms must therefore find ways of making both razor and blades lighter, which means thinner blades, more closely spaced, made of special materials, with new coatings.

So what does the future hold? With only five data-points, it is hard to be sure exactly which mathematical curve is being followed. If it is what is known as a power law, then the 14-bladed razor should arrive in 2100. The spate of recent innovation, however, suggests it may be a hyperbola. In that case, blade hyperdrive will be reached in the next few years and those who choose not to sport beards might be advised to start exercising their shaving arms now.