In the interests of clarity, the following chart taken from
Flight - December 2nd, 1943 is useful for comparing Schlaifer's manifold pressures, given in inches of mercury in his
Development of Aircraft Engines depicted above, with the equivalent boost pressures in lbs/sq.in. as used by the British. Schlaifer wrote
"Before the middle of 1940, a manifold pressure of 54.3 in. was authorized, giving a combat rating of 1,310 hp at 9,000 feet...". 54.3 in. Hg is the equivalent to +12 lbs/sq.in.. 1,310 hp at 9,000 feet operating at 54.3 in Hg. (+12 lbs /sq.in) is in agreement with the combat rating for the Merlin III given in
Alec Harvey-Bailey's The Merlin in Perspective, pg 155.
