The training scale, or training tree was first described in the 1912 German Equestrian Federation Official Training Manual, or Heeresdientsvorschrift, though not condensed down to the a list of six key components until decades later.  The training manual was intended to explain the basic training of a horse for any discipline, specifically - but not limited to - the Olympic disciplines of dressage, eventing and show jumping.

Since its initial publication the training scale/tree has spread from Germany around the globe and  been translated to multiple different languages.It has proven its effectiveness over and over in all equestrian disciplines.  
Tree or Scale?
The terms "training scale" and "training tree" refer to the same thing simply illustrated differently.  They are used the same way, and mean the same things.  Both are shown here.  I prefer the tree simply because it serves as a reminder that the qualities included are not in themselves the goal, they are a means of preparing a horse for specialized training in a particular discipline.
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Why are there so many different version?
The training scale directly below shows the original German terms.  These same terms can be found on the tabs across the top of the page.  On each of the linked pages the German term will be defined and discussed along with its most common English translation.  Unfortunately, some of these terms don't translate well.  Most variations in versions of the training scale stem from disagreement in translation, others from genuine disagreement about the process.

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Losgelassenheit
Anlehnung
Schwung
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