Normally, you can't do that as the compass will be too close to the metal and cause the compass to be off on the readings, but your on the right track.
Back in the Dish days I found 110 with a magic marker even before the satellite was turned on.
Found 119, found 110, then used a marker to mark the position on the Dish.
Set the Dish in the middle of the 2 marks, and when they turned on the satellite I had like a 60% signal.
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