 formula_6 was determined numerically, and is normally given as 0.028 if "I" is measured in megaamperes.However, it is also common to use 2.8 if formula_7 is expressed as a percentage.Given that the Troyon limit suggested a formula_7 around 2.5 to 4%, and a practical reactor had to have a formula_7 around 5%, the Troyon limit was a serious concern when it was introduced.