When I need a break from reading I flip through RTK3.
I noticed that some of the kanji in RTK3 do not appear to be all that useful! For instance, the book presents four “gate” kanji: 閃 悶 闇 閤. Of the four, the third I would rate as very useful (I come across it sometimes in my reading) and the first and second appear to be somewhat useful, based on what I see when I look them up in my dictionaries.
But the fourth one, 閤, looks to be virtually useless. It means “side gate”. It doesn’t appear to be used in any useful compounds. The only compound I could find after much digging is 閨閤 which supposedly means “bedroom”.
I wish I could have an annotated RTK3 in which the kanji that should be ignored, like 閤, are marked with an asterisk *. This would spare the reader a lot of wasted labor.