Someone is asked to write his birth year, the year of an important event in his life, his age, the number of years since the important event occurred—and then add these four numbers. The mentalist predicts the total, which will usually be the current year multiplied by two.
This force, according to Martin Gardner in his Mathematics, Magic and Mystery, 1956, p. 161, was included by Al Baker in Al Baker's Complete Manuscript, 1923. Stewart James, in commenting on this, reported that the name of the trick in this manuscript was “Thought Foretold” (see The James File, Vol. Two, Allan Slaight, 2002, p. 2212. The Baker manuscript, said by Gardner to be rare, does not appear in the comprehensive Secret Ways of Al Baker, edited by Todd Karr, 2003, but the force does appear there under the reported title "Thought Foretold", p. 749, copied from the notebooks of Eugene Bulson and dated July 1923.
Two years later, the force was marketed as “Buddhah Prophecy”, by Allan Lambie in The Linking Ring, Vol. 3 No. 3 [Sep. 1925], p. 43, as a single-effect manuscript (see James, above). Del-Ardo (Walter G. Magnuson) also marketed it around the same time, calling it “Twentieth Century Prophecy”. Other knockoffs swiftly followed. Robert Nelson released it under the same title used by Del-Ardo, "Twentieth Century Prophecy", n.d.; B. L. Gilbert released it as "Oriental Prophecy", c. 1926; Doc Nixon (William J. Dixon) included it in The Nixon Ghost Manuscript, 1929; etc.
Paul Curry cleverly embellished the presentation of the Date Addition Force in a piece called “Padding” in his booklet Something Borrowed, Something New, 1941, n.p., turning the prediction into a telepathy effect in which it is implied that the mentalist receives each of the spectator's four numbers as well as their total.