This TA is created with reference to the idea of Bollinger Bands % B, as known as "Keltner Channel % K" ,just saying.
With length of 20 and true length of 2.5, it looks to cover majority of stock price movements. For reversion to mean traders, this would suit them best because of its visual representation. 0.5 indicates mid band, 1 indicates price going outside of the upper band, and 0 means a breach of lower band.