This is the most precise one of all known methods, because it calculates the developed length dependent on the sheet thickness, the bending radius and the angle.
DIN 6935 method:
This is the most known one of all methods. By using the DIN6935 standard, it calculates the developed length dependent on the sheet thickness and the bending radius and is as a result of it less precise than the Oehler method.
User defined methods:
If both methods are not sufficient, the designer can define further methods by his own. By this, company specific standards can be included.