You better use your watch or your hobbs meter since the FAA may getcha on that +/- .1 where you may be off. It is extremely important to be exact as possible, God forbid you should be off juss a .1 or so off. In a perfect world that is, use a good faith estimate as the above poster mentioned. You are not going to be exact even if you did use that watch or meter, in no way is this going to come back and haunt you unless you should up to an interview with 1500TT and 1100 being in actual imc, that may raise a few red flags. If your flight was 3.8 and you think that 2 of it was in actual then by all means log the 2 hours of actual imc in your logbook.
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