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Typed in black ink on thin, off-white paper. The last page is handwritten in pencil on off-white paper. 18-page document containing data on the power efficiency tests carried out at the Powell Duffryn Electrical system between 12 April 1947 and 10th May 1947. Loose within pink/peach card file with other documents relating to Middle Duffryn and Bargoed High Pressure Station.
