I removed the problem - most of the time - by using actual weights. If the other person was heavier than standard weights then I'd limit fuel. Problem solved.
I always told my students why. Nothing like consistantly demonstrating a point to hammer home the lesson. None of this "Do as I say, not as I do" bulls**t from me (that I recall
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In Oz, standard weights are published for use in a/c with six seats or more.