Judson and Tom,
I could not resist to give you my input on this matter.
What is referred as “the German method” is actually an extract from our proof law. To the benefit of those who are able to read German ( at least Tom ) I have the original version attached. For those who are not, there is a babelfish translation where I have done some corrections attached as well. And last but not least I have attached a very simple basic translation.

But here is the original German language text which is base on the "Beschussgesetz", Anlage I der 3. VO
zum Waffengesetz, Satz 1.2.3:

„Der Mittelwert des Gasdrucks der Beschussmunition muss den zulässigen Höchstwert des Gasdruckes der Gebrauchsmunition Pmax nach den Maßtafeln, der Mittelwert des Gasdrucks der Beschussladung oder des Prüfgemisches den zulässigen Höchstwert der Gebrauchsladung oder des Gebrauchsgemisches um mindestens 30% übersteigen. Ist anstelle des Gasdruckes die Bewegungsenergie der Geschosse zugrundezulegen, so muss unter Verwendung eines gleichartigen Treibmittels der Mittelwert der Bewegungsenergie der Geschosse der Beschussmunition den zulässigen Höchstwert der Bewegungsenergie der Geschosse der Gebrauchsmunition Emax nach den Maßtafeln, der Mittelwert der Bewegungsenergie der Beschussladung oder des Prüfgemisches den zulässigen Höchstwert der Gebrauchsladung oder des Gebrauchsgemisches um mindestens 10% übersteigen. Kann mit der zur Verfügung stehenden Munition, der Ladung oder dem Gemisch die erforderliche Energie nicht erreicht werden, so ist unter Beibehaltung des Treibmittels ein Geschoss zu verwenden, dessen Masse um mindestens 10% höher ist als die der Gebrauchsgeschosse.“

Here is a translation using the babelfish webpage:
"The average value of the gas pressure of the proof ammunition must exceed the permissible maximum value of the gas pressure of the regular ammunition (Pmax) based on the listings in measure boards, the average value of the gas pressure of the proof charge or the test mixture the permissible maximum value of the regular charge or the regular mixture, by at least 30%.
If the kinetic energy of the bullets is to be taken as a basis in place of the gas pressure, then the average value of the kinetic energy of the bullets of the proof ammunition must exceed the permissible maximum value of the kinetic energy of the bullets of the regular ammunition Emax ( max energy ) based on the listings in measure boards, the average value of the kinetic energy of the proof charge or the test mixture the permissible maximum value of the regular charge or the regular mixture around at least by 10% using a very similar ( the same ) propellant.
If the necessary energy cannot be achieved with the ammunition, the charge or the mixture, that is available, then a projectile is to be used, which weight is at least 10% higher than those of the regular projectiles while maintaining the same propellant."

In short
a) the pressure of the proof load must be at least 30% higher that the service pressure.
b) if the energy is used as an indicator, the proof load must achieve a 10% higher energy that service ammunition while using a similar powder.
c) if the above is not possible than use a bullet which weight is at least 10% higher than service ammunition with the use of the same powder.
For example to c) Service ammunition .308 Winchester with a 150 grains, bullet pull the bullet and substitute it with a 165 grain bullet and use the same and same amount of powder.
The use of the energy ( as stated in b) as an indicated is not uncommon. I have used that at least two times with different German proof houses in the past. Recalculation of the energy back to the velocity gives you a very good indicator when you have reached the requested minimum increase of 10%.
I hope this helps a little bit on understanding the "German method"

best regards
Robert