Ed Anderson and others have mentionned at times that they observed power output variations at ground level and attributed the variations to variances in atmospheric pressures at ground level. Over the last few days, our area was subjected to very high atm press (approx. 30.5 in. hg.) followed by very low atm press. (approx. 29.4 in. hg.) At full power static runup, I noted 200 rpm less at low pressure.  I regret that I did not note the temperature and relative humidity.
Max rpm noted 5000. Sorel Airport elevation is 76 ft. Yvon.
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