1. a) C.N.S. Instruments, 61 Homes Road, London NW5
2. b) Sondicator, Automation Industries U.K., 108 Albert Street, Flect, Aldershot
3. British Standard 1811 (1973)
4. Dunlop, J. I., 1978. Wood Science and Technology 12: 49?62
5. Hearmon, R. F. S., 1966: Forest Prod. J. 16: 29?36