The research tree is fully interactive. You can move around it just like a map.
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Click and dragDrag anywhere on the tree to move the map around.
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Use the mouse wheelScroll the wheel to zoom in and out around your cursor.
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Focus a troop treeClick a troop-type research box on the map, or click its cost row on the right. In focused view, use the large focus panel to switch trees or return to Full Tree.