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Scott:

   If you think the errors I note which creep into the manifold pressure gage are bad, be aware that the standard run of Cessna/Beech/Piper tachometers are notoriously bad, frequently being off 100 RPM or more.  I once knew how to check the gyro using the hour meter based on an article I read.  The hour meter reads accurately (actual clock time) at a given RPM, and it is a weird intermediate value like 2357 RPM or some such.  If one starts a stopwatch when the hourmeter on the tach turns over to a new digit, and you track it for a half hour or so, one can measure and correct the error.  When my TR-182 was nearly new, I did such a check and found the tach reading 83 RPM low, and I placarded it as such.  I no nonger complained when it appeared to be turning about 100 RPM low on takeoff.  It was an instrumentation error.  So, in answer to your question: how do we set POWER if the manifold pressure and tachometer instruments are so much in error?  The answer is: VERY APPROXIMATELY.  Sorry, but it's true. Fred

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