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Why does the calculation for percentage profit vary based on whether a position is short vs. long?
Simple math: 50-25=25, hence decline from 50 to 25 is a 50% decline (you lose half), while an advance from 25 to 50 is 100% gain (you gain 100%, double your 25 to 50). Their point is that if you have more upswings than downswings - you'll gain more on long positions during upswings than on short positions during downswings on average. Again - simple math.