This technique was described by William Blau in his book "Momentum, Direction and Divergence" (1995). His book focuses on three key aspects of trading: momentum, direction and divergence. Blau, who was an electrical engineer before becoming a trader, thoroughly examines the relationship between price and momentum in step-by-step examples. From this grounding, he then looks at the deficiencies in other oscillators and introduces some innovative techniques, including a fresh twist on Stochastics. On directional issues, he analyzes the intricacies of ADX and offers a unique approach to help define trending and non-trending periods. Directional Trend Index is an indicator similar to DM+ developed by Welles Wilder. The DM+ (a part of Directional Movement System which includes both DM+ and DM- indicators) indicator helps determine if a security is "trending." William Blau added to it a zeroline, relative to which the indicator is deemed positive or negative. A stable uptrend is a period when the DTI value is positive and rising, a downtrend when it is negative and falling.