True, I was guessing, but I have always had a gas water heater. The stratification should not come as a surprise as I am familiar with sharp thermoclines in the ocean but I did not make the connection.

Right so far, but consider a thought experiment. After the first 20 gal of hot water has been drawn, the “bottom half” will be full of cold that the water heater is heating. But we know that there will be mixing, thus the hot water coming out after 10 minutes will be colder than the first gallon. Notably colder, because the tank is pulling in 50-60 degree water (typical in North America). And this will continue, so the “40 gal” capacity will be felt in the shower as exhausted well before 40 gallons of use.

This. My wife had legacy photos that her mother was unable to identify (dementia), and we were able to use ancestry submissions to figure out some of the unknowns.

I second this. I was a paper holdout for a long time, but ebooks (on iPad) is now my preference. Easy to carry and keep available (I use a man-purse for travel). Your library probably has ebooks to check out, so the app is free and the books are free. The kindle app also tracks simple statistics, so I use that to make sure I read daily.

Finally, material is important: you will read books you enjoy. Once you find an author you like, read their books. Series (serials) are good for this, too. Find topics, styles, and genres you like to engage and retain your interest.

Good luck. Enjoy the journey!