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Forty-Five degree measurements.

Forty-five degree fittings are now extensively used on not only steam and hot water heating systems, but also on hot water supply systems. The ability therefore, to take accurate measurements of forty-five degree offsets, has become a necessity. The problem is shown in Fig. 7. The distance A, between the centers of the two lines of pipe, is known, and the distance B is required. For offsets that are not greater than three feet, the following is a good rule, but is not close enough for long offsets. Add to the distance between the two parallel lines of pipe, five inches for each foot of such distance, and at the same rate for fractional parts of a foot. This would mean the addition of 5-12 of an inch for each inch. To be more exact, add 13-32 of an inch to each inch of distance between the centers of the two lines of pipe. The correct method is to multiply the distance between centers by 1.414. The latter is the preferable computation for long offsets.

This was taken from the book "Questions and Answers on the Practice and Theory of Sanitary Plumbing, Volume III, Practical Wrinkles", which was published in 1919.

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