Indicator cleanly displays when price closes beyond the last high/low zigzag.  This is important to confirm a trend is evolving in a healthy manner:

“To confirm a trend is evolving in a healthy manner, not only do we need to see price moving higher/lower than its previous high/low, we also expect to see at least two closes beyond that high/low as further evidence that the market is accepting and building value. Failure to see at least two closes may be a precursor to what’s often referred to as false breakout, and while the move still holds its merit to qualify as a new high/low in the cycle, the quality of the leg is poor in nature.”
– Ivan Delgado

For more details on validated zigzag legs and market structures, check out this article: 
How To Read Market Structures In Forex