When does a trend commence?
When it starts establishing higher highs and higher lows (uptrend) or lower highs and lower lows (downtrend).
When does a trend finish?
An uptrend ends when it stops making higher highs and higher lows (objective), when it leaves the upward trendchannel (subjective) or when it diverges negatively with momentum indicators like the Slow Stochastic (early warning).
A downtrend ends when it stops making lower lows and lower highs (objective), when it leaves the downward trendchannel (subjective) or when it diverges positively with momentum indicators like the Slow Stochastic (early warning).
When a trend ends it doesn't necessarily needs to reverse. It can move into a range of non trending patterns (triangles, broadening formations, flags, pennants, wedges or rectangles).
What does that mean for today's AEX?
We are currently in an uptrend with higher highs and higher lows.
We would end that uptrend below the last low 332,37 (objective) or when it leaves the upward trendchannel at 337,50 (subjective). Since Price and Slow Stochastic diverged negatively between the September 21 high and the October 14 high we already have had an early warning of a trend end.