My grandfather's brass vernier scale sextant (circa 1910, no micrometer drum).
My aunt wanted to make it into a lamp. My cousin complained loudly, demanding that she pass it on to me, a Naval officer.
Aunt Lucy surrendered and sent it to me.
It was in rather sad shape, but I cleaned, calibrated, polished, and repainted it and refurbished its lovely walnut case.
So it sits in grandeur on my side table and I do occasionally take it out and take a sight. It works, just fine.
But sight reduction is a pain, even with software. GPS is a lot easier.
Beside it is a replacement for my Keuffel & Esser Log Log Duplex Decitrig slide rule.
The original was given to me in high school by Mr. (Stempel?), a next door neighbor who was an electrical engineer and had a beautiful daughter. I don't know whether he was mentoring me to be an engineer or grooming me for his daughter. The first won and off we went to Duke Engineering School.
But a really cool guy. Thank you again, sir.
Absolute magic, except I could never keep the decimal point straight.
That problem was solved with my first calculator, the HP-35:
I was convinced that little green spacemen had sprinkled magic microchips under the polka-dotted mushrooms of Monterey county that were being harvested and put into a box by Hewlett Packard.
As I said, I was having problems with decimal points. There was a Brazilian officer in my class who was kind. So one day I just asked him.
"Look: I'm as smart as you, but you're getting A's and I'm getting C's. What am I doing wrong?"
He said, "I've been watching you. Basically you are totally disorganized. Here: you need one of these:"
"You need to organize your writing, draw boxes around your answers, using this ruler, and get a calculator, like this one." and held up his HP-35.
Dashed into the office, slapped down the VISA and said, "Please, get me one."
And indeed, it worked. I got a "most improved" award on graduation. Not too hard, since my Duke BA got me a 2.11 and Monterey got me a 3.72...
I now carry around a modern HP-35s.
And still carry the C-Thru, an engineer's pencil, its separate eraser, and have a pad of green grid paper on the shelf under the coffee table.
More as an act of faith and of following the engineer's Articles of Religion than for any practical utility. They just make me feel good, like a reel injuneer.
Maybe I should go after eBay and see if I can find another of the reel thang HP-35.