Percentage and point moves
Why does the same dollar move in BTC mean different things depending on its price level?
In plain words
A point move is a change in an asset's price measured in currency units; a percentage move divides that change by the starting price. Both describe the same event, but the percentage tells you how large the move was relative to the price you started from.
Why it matters
Point moves describe how much a position gained or lost in money terms. Percentage moves describe how difficult the move was to survive and how much of your capital it consumed. Comparing point moves across periods when the price level differs can make one period look calm or wild for reasons that have nothing to do with actual risk.
In a real week: BTC, week of 30 July 2018
In the week of 30 July 2018, BTC opened at 8210.99 and closed at 7024.19, a return of -14.45%. The week's high was 8273.0 and its low was 6882.29, a range of 20.21%, and BTC sat 40.09% below its 52-week high. The same point drop from a price half as high would have been roughly twice the percentage loss.
A common mistake
Treating point moves as a measure of risk on their own. A large point move in an expensive market can be a modest percentage change, and vice versa; risk is usually better judged in percentage terms.