I am adding a link to this old topic and have also copied a post in from the same topic.
Martydallas
Nov '16
I have and able to harvest twice this past season. Both times I only had 15 or 20% of the cells capped. Yet after harvesting it was all under 18% moisture. I did purchase a refractometer to test.
My mentor suggested taking the frames out and shaking them in if no honey came out that it was likely at the correct percentage. I did that about a week before I harvested, and in fact no honey or moisture came out of the cells. Therefore I felt comfortable harvesting. And after harvesting I did test each of the frames for its overall moisture content.
In fact my 2nd harvest set uncapped for a good month prior to me harvesting because we were about to go into winter I decided to harvest. And it was closer to 16.5 to 17% moisture.