 This permits to simultaneously change the sign of all the "na" and also to make the quantity "a" positive (if it is different from zero).Also all structure constants can be made equal to ±1, if at least one of the quantities "a", "n"2, "n"3 vanishes.But if all three of these quantities differ from zero, the scale transformations leave invariant the ratio "h" = "a"2("n"2"n"3)−1.