Audemars Piguet's Royal Oak is one of those famous watches. The style has been around forever, and AP's watchmakers are constantly ramming crazy new features and innovations into it. This year, they made it open-worked, which means you can see through the movement from top to bottom—a real challenge when you consider all the structural and mounting considerations you need to take into account when putting a multi-hundred-part machine in the middle of something you can strap around the smallest part of your arm.
The coolest part of this watch, though, is its double balance wheel: that small golden circle in the lower-right corner of the photo above. The balance wheel is one of the key places a watchmaker can adjust a timepiece to make it more accurate. The wheel itself is studded with eight tiny, horseshoe-shaped weights. Turn the horseshoe so that its closed end faces either the inside or outside of the wheel, and you're shifting a very small amount of mass, gently influencing the spin out accelerate of the wheel.
The to a greater extent of those weights you have, the to a greater extent exactly you fire decide the watch's speed. You could barely arrange A big be bicycle inwards the movement, providing to a greater extent board for weights around its perimeter, but, again, there are those space considerations. In order to keep its movements small, AP just stacked two balance wheels on top of each other. Voila, twice the number of weights. Added bonus: You can see the top balance wheel through the face of the watch, and the bottom one through the back. The stainless steel version will run you $44,100.