Math: 1835

A great variety of multiplication tables were mentioned, extending, in some cases, as far as 1,000 times 1,000: these were computed and printed at enormous expense and labour by the English Board of Longitude, the French Board of Longitude, and by the Prussian Government.

Since there weren't calculating machines, doing repetitive or complex numerical calculations was extremely time consuming. To make things faster, people would use mass-produced, printed mathematical tables. But there were problems, especially with tables that were new, or had to be updated often:

The lecturer next proceeded to furnish proofs of the extensive errors by which all existing tables were at present vitiated, and observed, that from the chances against an error being detected, it might reasonably be assumed, that for every error actually detected, a multitude of undetected ones must exist. In a single page of one set of nautical tables, he showed about fifty errors: in other sets of tables, a single individual had detected in some five hundred, and in others one thousand errors.

 Imagine a world where even math was iffy!

--From Arcana of science and art--