Word on BIOPACE
Please understand that this is not Biopace technology. Shimano created Biopace with the completely wrong orientation of the biggest radius of the oval. Instead of positioning it in power zone which is slightly below the level of the crank, they clocked it to the dead zone where human generates least power. The result was that in power zone pedaling was too easy and in dead zone very difficult. Exactly opposite to how it should be.

Round rings do not optimize the way humans produce power

Other elliptical chainrings
Clocking (timing) and shape of the oval are the most crucial parts of the design. Ride quality of Absoluteblack Oval ring will be different to ovals from brand X or Y. 2 years of development of our ovals resulted in commercially most successful product of its kind. AbsoluteBlack is the First company who managed to successfully popularize ovals in mountainbike sport. Please note: Other manufacturers offer one timing and ovality setting for all chainring sizes, but pedaling behavior changes with each size considerably. To optimize for this, every chainring size needs to be a bit different. For example the smaller the chainring size the bigger the ovality has to be to help climb steeper hills more effectively. This is where we specialize in and optimize every size to particular pedaling style. This is also why we do not provide information about timing and exact ovality of the chainring as each one is different.

Mounting instruction:

Generously grease the waved shape of the crank arm, then put the chainring so that fits completely(convex side to the crank arm). Put small amount of 17px strength Loctite on the lockring threads and tighten it with torque of about 47-54 Nm.

You will need "Cannondale Hollowgram Spider Removal Tool KT012" or similar to open and close the lockring. 

Comparison chart:

XX1 spider + XX1 ring: 28T(69g), 30T(81g), 32T(84g), 34T(91g)
AbsoluteBLACK chainring: 28T(55g), 30T(56g), 32T(57g), 34T(70g)