How a foil touch becomes an electrical signal
The point does more than make contact: it acts as a tiny switch. When a thrust presses the spring-loaded plunger far enough, the switch closes a circuit. A wire running along the blade carries that change to the fencer’s body cord and then to the scoring apparatus, which signals that a touch has landed.
The resistance to pressing the point matters. A blade can brush or tap an opponent during fast movement; requiring roughly 500 grams of force helps keep those light contacts from counting as completed hits. The mechanism turns a fleeting physical touch into a signal the scoring system can distinguish.
Why contact alone is not enough
Foil scoring also depends on where the point lands. The valid target is covered by a conductive jacket, called a lamé, connected to the scoring system. A point closing its circuit against that jacket produces a valid-touch signal. Contact elsewhere can trigger an off-target indication instead, but does not score.
That division of labor is the key to the design: the button detects a sufficiently firm thrust, while the conductive target identifies whether it landed in the right place. A hit that looks identical to an observer can therefore produce a different result at the scoring box, depending on both pressure and location.
