The Gartley pattern was proposed by H.M. Gartley in his book Profits in the Stock Market. The Gartley design is also known as Gartley 222 since it is mentioned on page 222 of the book.

As a result, the Gartley pattern is the first known harmonic pattern, and all subsequent harmonic patterns are developed from it. Let's look at the legs in the Gartley configuration now:
XA: This might be any move on the chart; there are no particular prerequisites for this motion to be part of a harmonic pattern.
AB: This motion is the opposite of the XA move and should be approximately 61.8% of the XA move.
BC: This price movement should be the opposite of the AB movement and should be 38.2% or 88.6% of the AB movement.
CD: If BC is 38.2% of AB, then CD should be equal to 127.2%(extension) of BC's price movement. If BC represents 88.6% of AB, then CD should represent 161.8% (extension) of BC.
AD: The total price change between A and D should equal 78.6% of XA.

Free Harmonic Patterns is an indicator which displays up to 7 types of patterns (ABCD, bat, butterfly, gartley, shark, crab and deep crab) detected on higher timeframe charts (H1-D1). The ABCD (or AB=CD) pattern is composed of three movements and four points.

https://fxmerge.com/free-harmonic-patterns-indicator