Firstly, 4200 is the current level of the 40 week moving average, an indicator which has been a good guide to the trend (if any) of the ASX 200 for the past decade, as shown on the following chart, and indeed since long before that. To retain confidence in the fledging down trend taking flight, the market needs to push downward through the trend line drawn from the 2009 low, and do so while remaining under the 40 week moving average.
Secondly, at 4210 lies the Fibo 50% retracement of the decline from the May high, at 4210, as shown on the following 4-hour candlestick chart. Trending moves are often followed by corrections in to the Fibo zone (38.2% to 61.8% retracement) before the trend resumes. Can't help but mention, what a beautiful 5 wave move down from the May high, which in Elliott Wave terms defines the trend as down. No labels, but easy to see.