Look at the VWAP - 121.97 http://stocknessmonster.com/stock-trades?S=UMC&E=ASX
I just pasted that page into Excel - 1.02m shares changed hands between 10am and 1pm at around or above yesterday's closing price.
Someone saw a weakness in the buy depth at 1pm, exploited it and panic followed. The weakness is understandable as 1m shares changing hands is historically a lot for this stock and can explain the exhaustion, especially following a 1.5m day the day previously.
In the last 6 months, excluding today and the cross-trades, UMC has had over 1m volume only 6 times, so that is a pretty decent number for this stock.
The XJO dropped like a stone on opening, and yes it did spike down around 1:30, but from 10:10am it looked like a bad day.
So I don't know if this is some crackpot theory, and I must admit here on HC after a stock has had a bad day everybody cries conspiracy, but I do happen to think that somebody judiciously dumped around lunchtime and caused a panic.
UMC Price at posting:
$1.15 Sentiment: Buy Disclosure: Held
