Math is some bullshit. Seriously, I have insane math anxiety. In first grade, my teacher got pissed at me for not understanding subtraction.
She met me nose to nose.
"How many fingers do you see in front of you?" she asked, taking my hand and holding it in front of me.
"Five?" I asked, tears already flowing.
"Now, take those away," she said, making me put my hand behind my back, "and how many are left?" At this point there was spittle collecting in the corners of her mouth.
"F-f-f-five?" I stammered, weeping openly.
By now you might have guessed that I love calculators. They are beautiful. But they run out of power, are made of plastic, and aren't cool, lasting, free energy devices that might emerge in an open, post-civ market environment. Given that civilization is unsustainable, then the gadgets produced by the institutions of civilization are not always likely to be sustainable either. But long ago, a gadget was made that could crunch numbers fast, and you could basically own all your life and pass on to your kids: the slide rule.
I don't own a slide rule. Nor do I know how to use one. But I'm gonna get one, and I'm going to learn how to use the damn thing. Why?
There is an ethos behind old gadgets, and that is sustainability. A cast-iron pan will last a couple of centuries if taken care of. A slide rule will last generations. Hell, you can even make one yourself. And just in case the shit does, in fact, go down, then it wouldn't hurt to know some old school methods of crunching numbers in the event of rebuilding and such.
This is strongly applicable to the awesome gadgetry we will have the opportunity to make in a post-civ environment. I don't want to "go back" to anything, per se, what I want is to redevelop an understanding of responsible, sustainable technology, and begin looking at ways in which we can create devices that will combine the ethos of past technologies, with the brilliance of the future.