A new and up-to-date edition of this book has been long overdue and I am grateful to Mr. VV. H. Coulthard for his co-operation and assistance in preparing the revised edition for the press. I also wish to acknowledge my indebtedness to various aircraft instrument manufacturers who have kindly provided information and data concerning their instruments as well as photographs and diagrams for reproduction; also to the Air Registration Board for permission to reproduce their Category "X" syllabus; to the British Standards Institute for allowing quotations from the British Standard Specifications; and to Mr. T. W. Paddon and Mr. C. J. Simmonds, A.F.R.Ae.S., of the British Institute of Engineering Technology for useful suggestions and the specimen examination questions reproduced in Appendix XI.
