Werepuppy's A Doll A Day Challenge 2020

[davidd]

Definition: In old naval slang, an X-catcher or X-chaser was someone who was good at math—literally someone good at working out the value of x.

I wonder in which era and which navy.  "Mental Floss"'s "x" page is interesting, but that's not a term I've come across before.  I wonder where they got it.

Primarily in the Royal Navy of the UK, early 20th century.

The term was apparently in common use circa 1907, when it was used in a letter by an applicant to Robert Scott's Antarctic ex-pedition: source

Another corroboration of early 20-Century usage suggests the term was still in use during the era of air travel: source

Another primary source use of the term is in the novel, Pincher Martin, O.D.: A Story of the Inner Life of the Royal Navy by "Taffrail," published in 1916 by W. & R. Chambers, Limited of Edinburgh: source 

The term appears near the middle of Chapter V:
He was an x-chaser, in that he had done remarkably well in all his different examinations; but besides being an ex-pert theorist, he was an officer who knew the practical side of his business from A to Z.

(In addition to meaning someone who is good at mathematics, the term "x-chaser" also applies to anyone who strives to achieve excellence across a variety of fields.)