The Margin Bridge Builder

Explain exactly why our margin changed between these two periods.

Period 1: [REVENUE, COSTS, VOLUME, PRICE, MARGIN]
Period 2: [REVENUE, COSTS, VOLUME, PRICE, MARGIN]

Build a margin bridge that decomposes the change into:
1. Volume effect
2. Price effect
3. Mix effect (if multiple products)
4. Input cost / variable cost effect
5. Fixed cost / operating leverage effect

Show each effect in dollars, reconcile them back to the total margin
change, and tell me the one or two factors that drove most of the move —
and whether they're within our control.