1. ‘British Standard Code of Practice’, CP 1003, 1964 Pts 1, 2 & 3
2. Takeuchi, T.: United States Patent, (3,603,954)
3. ‘B.A.S.E.E.F.A. Certification Standard’, SFA 3007,
4. Taguchi, N.: United States Patent, (3,631,436)
5. Ultramarine Instruments Ltd., Patent applied for.