Definition of "elementary, my dear Watson"

The possibility of signaling to to the planet Mars is merely a question of elementary mathematics. […] It is such a simple little problem that any one should be able to take a pad and pencil and work it out in ten minutes. "Elementary, my dear Watson," as Sherlock Holmes was wont to say. "Elementary."Originally published in the Rochester Post-Express.

1909 August 24, “Signaling to Mars. An elementary problem, says Professor [Edward Charles] Pickering, of Harvard.”, in The Times Dispatch, number 17,992, Richmond, Va.: [Times-Dispatch Pub. Co.], page 6, column 7

"I fancy," said Psmith, "that this is one of those moments when it is necessary for me to unlimber my Sherlock Holmes system. […] Do you follow me, Comrade Maloney?" / "That's right," said Billy Windsor. "Of course." / "Elementary, my dear Watson, elementary," murmured Psmith.

1909 October – 1910 February, P[elham] G[renville] Wodehouse, “In Pleasant Street”, in Psmith Journalist, London: A[dam] & C[harles] Black, […], published October 1923, page 140

What have we for lunch? Stew? How did I know? Elementary, my dear Watson—the smell of onions is unmistakable.

1922 January, Agatha Christie, “Annette”, in The Secret Adversary, 1st American edition, New York, N.Y.: Dodd, Mead and Company, published 1922, page 191

Elementary, my dear Watson! There's an invisible element in the cabinet, a character that, without making itself known, gives coherence to and makes systemic all the braying of the government team. A boss to whose command everyone submits.

1995 June 30, Subcomandante Insurgente Marcos [pseudonym; Rafael Sebastián Guillén Vicente], “Subcomandante Marcos: 1994–1996 – Spreading the Word [The Tale of Durito’s Return]”, in [anonymous], transl., edited by Žiga Vodovnik, ¡Ya Basta! Ten Years of the Zapatista Uprising: Writings of Subcomandante Insurgente Marcos, Oakland, Calif.; Edinburgh: AK Press, published 2004, page 175

"Seems like you've got it all figured out, but if I was FBI, why would I go in alone and risk my life to save you? Why wouldn't I call in the troops and end this once and for all?" / "Elementary, my dear Watson. You don't know who to trust either. You're in the same position as me. […]"

2012, Ethan Cross, chapter 37, in The Shepherd, London: Arrow Books, Random House, part 3 (The Rod and the Staff), page 201