I own a couple of 8.5-x-11-size paperback books, each containing 200 “Sunday” crossword puzzles from the New York Times. I am working on one of the puzzles at all times, here in the UAE. Just as I did back in California.

I have reached two conclusions about the Sunday NYT puzzles. The important one will be the second.

One is … that I wonder how all of these actually are “from the pages of The New York Times,” as it says on the cover of the book.

Just doing some arithmetic here, and 200 puzzles is nearly four years of Sundays. The volume in front of me is No. 10 — meaning 2,000 puzzles have been sold “from the pages of” … but 2,000 puzzles takes us back about 38.5 years. Which would make for a lot of cultural questions badly out of date. And also would mean we ought to be bumping up against “Nixon’s first Labor secretary” kinds of questions.

Many references in the Sunday NYT puzzles are dated … but not that dated.

Thus, I tend to believe the puzzles are sold to NYT as Sunday puzzles, and could have been “from the pages of” … but probably not all really were.

Second, and this is the point of this entry …

I am using the NYT Sunday puzzles as a sort of “canary in the coal mine” of my brain.

As someone suitably impressed by how difficult the puzzles can be and how they test both vocabulary and punning ability and spelling … I have decided that as long as I can successfully complete 98 percent of every puzzle, I’m not losing it.

This is important to me. We get old. We start to lose our mental edge. But how can we know? We can see ourselves getting weak or feel ourselves getting frail, but how do we judge a mental decline from inside that declining mental edifice?

By the NYT Sunday crosswords.

These are not easy. Clues calling for knowledge of French, Spanish, German, Latin. Lots of topical clues. And many more of in which the clue is cleverly (but not incorrectly) obtuse.

“Union member since 1896.” That could be an AFL-CIO question, maybe. But what it is asking for, in four letters, is the U.S. state that entered the union in 1896, and the answer is Utah.

“Pressing need,” five letters? Steam.

“Negative north of England,” three letters? Nae.

“Swab,” four letters? Tar.

“PX users,” four letters? NCOs.

And so forth. Those come from the puzzle, No. 174, that I am about halfway through.

Often, clues are so devilish that a hole quadrant of a puzzle resists me for hours, days even … and then while staring at it for the 20th time, suddenly a light bulb goes on inside my decaying brain … and there is the key breakthrough. Everything else falls into place.  I often find myself thinking, “Where did that come from?” What synapse pulled that answer from what deep recess of my brain?

Puzzle solved. Or nearly so. Perhaps one letter off a grid 21 (or 23) boxes wide and deep.

The NYT Sunday crosswords test me. They sometimes exasperate me. But at the end, I beat them, sometimes perfectly.

If/when I’m not as mentally nimble as I once was, I’m not sure I will know it, on an hour-to-hour basis.

But when the NYT Sunday crosswords begin to stump me … I’ll have an idea that something is going on. It may not make me feel better, but at least I will know.