It's important when comparing the volatility of different securities that a like-for-like comparison is being made. The volatility of one security calculated using daily data cannot be compared against a second security if the calculation for the second securities volatility has been made using weekly or monthly data.

Typically, to make comparisons easier, volatility is most often quoted on an annualized basis. There are usually about 260 trading days in a year, so Bloomberg defaults to 260 trading days. Because volatility is based on standard deviations, which in turn is calculated by squaring data, a daily standard deviation number must be multiplied by the square root of 260 for it to be translated into an equivalent annualized volatility number. Weekly volatility data must be multiplied by the square root of 52 for it to be annualized and the monthly volatility data is annualized by multiplying it by the square root of 12.