A tachyon meter was a device used to detect tachyons. One was carried by the Time Agent Jack Harkness, who used it on the RMS Titanic in 14 April 1912; feigning a tachyon reading in John Hart's closet, Jack used the opportunity to shove John into the closet and lock it, making off with a diamond and John Hart's vortex manipulator. (AUDIO: The Death of Captain Jack)

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