"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 Colonial 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.

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