~当たり (per unit)

The United States emits a quarter of the world's carbon dioxide, and its per-capita emissions are also the highest in the world.

There was no problem performance-wise, but the cost per unit was just too enormous, so the cost-performance was poor.

The length per one degree of longitude at the equator.

Even when you make international calls from a cell phone, with Mobila you can call for '20 yen per minute.'