Actually there was not a emperator or an international meeting that established that the so called 'normal tension' or medium tension mean that the strings must have exactly that value of Kg for all the string brands: actually it is like the quantity of sugar teaspoons for the cappucino: which is the the quantity' that for most of people meant that it is the medium qquantity? Not too sweet, nor too bitter?
When one string brands taken the decision to make guitar strings the problem to define the medium tension was taken in a easy way. The set was tested by an extensive quantity of players and, from their feedbacks, the brand taken the final decision. In other worlds, it is question of statistic. We, in the far past, done the same thing and dicovered that our medium/normal tension was more or less the same of Hannabach medium tension set.
Said that, it is also true that there are the so called medium tension nylon gauges that are always those that the big guitar manufacturer order to us, to Dupont and to somebody else: .71mm; .81 mm; 1.01 mm. Instead, an high tension are: .73; .83; 1.03 mm.