Anthony Lane, in his superb essay on the Leica 35mm camera, hits on a definition of something I've always found difficult to express. After calling Leica cameras "the most beautiful mechanical objects in the world," he writes:
Many people would disagree. Bugatti fans, for instance, would direct your attention to the Type 57 Atlantic, the only car I know that appears to have been designed by masseuses. Personally, I would consider it a privilege to die at the wheel of a Lamborghini Miura—not difficult, when you’re nudging a hundred and seventy m.p.h. and waving at passersby. But automobiles need gas, whereas the truest mechanisms run on nothing but themselves. What is required is a machine constructed with such skill that it renders every user—from the pro to the banana-fingered fumbler—more skillful as a result. We need it to refine and lubricate, rather than block or coarsen, our means of engagement with the world: we want to look not just at it, however admiringly, but through it. In that case, we need a Leica.
The money line, for me, is the one about mechanical gadgets that I've bolded here. I would add that the perfect device has mechanisms that are all (in principle) visible, so that their workings themselves can acquire their own beauty. The beginning of the twentieth century was a great moment for such devices -- besides the handheld camera, there's the typewriter, the bicycle, and hordes of small, handheld, nonelectric gadgets, like Duchamp's chocolate grinder (above).
Our moment is the digital one, but the one that I and most people alive today were born into is the intervening one dominated by predigital electrical and fuel-powered appliances -- the refrigerator, the automobile, the blender, the electric typewriter, the blow dryer, the lawnmower, etc. But I love anything mechanical that endures from that pre-electrical epoch (or which doesn't partake of it) -- the water handle and the flush toilet, can openers, hand-cranked mixers, etc. There's a fantastic scene in Vittorio De Sica's Umberto D that centers around a girl, a cat, a match, and a coffee grinder -- it has to be seen to be believed. Track it down.