10^-5 + 10^-5 = 2 * 10^-5

10^-5 * 10^-5 = 10^-10

Therefore, (10^-5 + 10^-5) - (10^-5 10^-5) = 2 10^-5 - 10^-10 = 1.999999999 * 10^-5