This principle takes advantage of a positional number coincidentally matching the value of the card resting at that number to count down and locate a selected card. The first published instance of this principle is “The 'Impossible' Location” by George C. Kaplan in Hilliard's Greater Magic, 1938, p. 269.

Jacob Daley, on p. 7 in his second notebook, c. 1937, recorded “Vernon's Index Key Mental Effect”, which begins with the use of a coincidental match of card value and position. The application by Vernon results in the location of a selection, but in a less direct manner than the count-down in the Kaplan effect. Daley attributes the use of “the 'natural' key” to Arthur Finley. This attribution complicates the crediting of the principle. That said, Kaplan maintained his claim to the “natural card” principle ten years after the publication of Greater Magic, in his Fine Art of Magic, 1948, “Au Naturelle”, p. 48.

In Greater Magic, there is a note after Kaplan's trick that mentions a related telephone test by Al Baker and Audley Walsh. This trick, “Number, Please”, was originally marketed in 1935; see The Secret Ways of Al Baker, 2003, p. 568. It uses the matching of a number with a card value to cue the location of a selected card. However, the match has been deliberately produced by the procedure and cannot be said to have arisen by coincidence.