It can be a bit surprising how long it takes people to spot mistakes. In looking through the publications of the Board of Longitude, for example, I recently found one that seems to have gone unnoticed for 136 years. This was in a copy of Charles Hutton's Tables of the Products and Powers of Numbers (1781) that belonged to the Royal Observatory.
While Hutton's tables are not, to be honest, a gripping read, it was important that they should be accurate. But it was only in 1917 that one of the Observatory's staff added a note that some of the figures were wrong:
This helpful soul was, I think, Thomas Charlton Hudson, Assistant in the Nautical Almanac Office from 1893 to 1923, who also rightly crossed out the offending figures.
I'm rather intrigued by this. Had the tables been in regular use at the Observatory since 1781? If so, why did it take so long to spot the mistake? And had this led to errors in other calculations in the meantime? If not, what was going on in 1917 that finally brought it to light?
In any case, I am rather reassured that Hutton's book was still in use so long after it was first published.