A very useful thread
I realise that I am posting a reply to an old thread, but I came across it while searching for the answer to a question about the relationship between boost, throttle and pitch - Len Deighton, in the afterword to his magnificent novel 'Bomber' mentions having had it explained to him by (if I remember correctly) the pilot of an He111, but he does not explain in in his afterword!
I am not a pilot (I did some flying towards a PPL back in the 1980s but had to give it up for lack of money!), but I have always loved aviation and flying. I am by profession an engineering consultant, and would like to mention that when we talk of pressure it is either referred to as 'gauge' or 'absolute'. Most pressure indicators found in industry show 'gauge' pressure, i.e. they will read zero at normal sea level atmospheric pressure. So it seems correct to think that a boost gauge will read zero when at rest, whereas manifold pressure, which is an absolute pressure, will be indicated as a positive value (which will vary according to local conditions, altitude, etc.)
Oh, and having read this thread in its entirety, I do now understand the relationship. I can re-read my Lancaster and Spitfire pilots' notes with new insight!