Free cotton armor recruits approximately 1 Puma Spearman for every 2 minutes of game length, up to 30 minutes.
—In-game description

Barometz is a Big Button technology in Age of Empires III: The WarChiefs that is unique to the Aztecs and can be researched at the War Hut once the Commerce Age is reached. Once researched, one Puma Spearman for every two minutes the game has passed, up to 30 minutes (for a total of 15 Puma Spearmen), will appear in the Home City shipment point.

Puma Spearmen cost a total of 100 resources each, meaning this technology is cost-effective after 16 minutes of in-game time, at 8 Spearmen shipped.

With the Industrial Age Old Ways Home City shipment, the cost is reduced to 375 coin.

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