actually, you need just some smart ideas to miniaturize a single full adder unit (built up by 2 XORs and 2 ANDs). nevertheless, it was a long way to this final minimized form (you can see all the steps from my first 10bit calc which nearly used the whole space, to 16bit adder, to 84bit adder and now 144bit), but it was more a topological problem to arrange and to wire this stuff rather than to think about how to solve a problem like "how to build a stable and reliable binary to decimal converter which fits to the screen". the rest of the 144bit calculator is just copy and paste and a little bit of wiring. in that sense, it isn't more complicated than to build a 1bit full adder in this size. i'm just got bored and decided to build the biggest adder possible in PT.
on the other hand, for my 4bit decimal calculator i needed more brain power. simply because there were much more problems to solve: a small decimal to binary converter, a small 4bit adder, a small decimal to binary converter, preventing missfires of the converter to the display, so the display converter doesn't get flood with uran (old version) or sparks (new version), a fast but small display converter and, of course, a simple and understandable design for everyone (yeah ... maybe most of you :D ).

coolest: (click here)
most sophisticated: (click here)

The best one I've ever made is the water powered factory which isn't very impressive but it's good enough I think

I have made the Salt Extractor! It extracts it from salt.

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my fail of a water filter was probly most complex and it didnt even work!

btw devest8a your logo looks a little like toby maguire. is that really him?

Either my compact 7-seg 0-9 counter or my neutron-powered, photon-assisted, hybrid acid-noble fueled flamethrower.

Counter:
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Flamethrower:
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I made a car using the old powder toy
you can see it if you type in "basic car" in the new powder toy