Specification for Metric Typographic Measurement. BS 4786: 1972. 8vo, 21cm, 10p (2 folding), British Standards Institution, 2 Park Street, London, 1972.
Two folding pages; grey paper wrappers, titled in black. A fine copy.
'It is recommended that the existing heights of type be retained but expressed in millimetres. For example 0.918 in = 23.317mm.' That's a relief, then.