Input: Revenue $10,000, cost $6,000.
Result: Profit $4,000, profit margin 40.00%, markup 66.67%. The same $4,000 looks very different depending on whether it is measured against revenue or against cost.
Input: Revenue $48, cost $30 for a single product.
Result: Profit $18, profit margin 37.50%, markup 60.00%. A trader who marked up 60% and assumed a 60% margin would be short by more than a third of the profit they expected.
Input: Revenue $250,000, total costs $175,000 including overhead.
Result: Profit $75,000, profit margin 30.00%, markup 42.86%. Because overhead was included, the 30.00% here is a net margin rather than a gross one.