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Printed in black, pink, green and yellow ink on off-white paper. A graph charting steam flow and pressure curves at Cefn Coed Colliery for Monday 23rd June, 1930 and Tuesday 24th June, 1930. Loose within a green card file with all other documents with accession number 83.184I/67. The file is labelled 'Colliery Boiler Plant B31', 'Cefn Coed Data' and 'Colliery Engineering'.
