There is a fault line running through written numbers, and it hides in a single keystroke. Write the quantity "1,5" and half the world reads it as one and a half, while the other half reads it as fifteen. The decimal separator, that small mark between the whole part and the fraction, is not the same everywhere, and the gap between the two readings is the kind of ambiguity that quietly wrecks invoices, recipes and spreadsheets.

Both marks are ancient, and neither is an upstart. The point and the comma were both pressed into service by early modern mathematicians feeling their way toward a notation for fractions; the works of Napier, among others, used them side by side. There was no original sin, no single correct choice betrayed. Instead, as the practice settled, different parts of the world simply settled differently. The English-speaking countries came to rest on the point, while much of continental Europe adopted the comma, and each grew so used to its own convention that the other now looks like a mistake.

The honest position, and the one the exhibit takes, is that there is no right answer to appeal to. International standards bodies accept both marks; there is no arbiter who can declare the comma wrong or the point superior. What there is, instead, is a permanent need for care. A number stripped of its context is genuinely dangerous, because the same three characters can mean two things ten times apart, and nothing in the digits themselves tells you which. It is a rare case where the ambiguity is not in the meaning of a word but in the punctuation of a number, and where getting it wrong costs real money in the real world.