The ratio can be determined in relation to F stops since each increase in f-stop is equal to double the amount of light: 2 to the power of the difference in f stops is equal to the first factor in the ratio.
The ratio can be determined in relation to f-stops, as each increase in f-stop is equivalent to double the amount of light: 2 raised to the power of the difference in f-stops equals the first factor in the ratio.