Other mistake: Magnum and Vivian are not listening to the TV at loud volume (they have a quiet time watching and talking without raising their voice), but Higgins, all of a sudden hears it all the way from the main house and is greatly bothered by it.
Magnum, P.I. (1980)
1 other mistake in Letter to a Duchess
Starring: Tom Selleck, Roger E. Mosley, John Hillerman, Larry Manetti
Don't Eat the Snow in Hawaii - S1-E1
Continuity mistake: When Magnum drops the ring out of the envelope, nothing is near it as it's shaking. In the close up shot, it's next to keys. (00:44:20)
Mac: Time has little to do with infinity and jelly donuts.
More trivia for Magnum, P.I.