Quote from flyingforget:
look at the chart ,the volume is constant,am I wrong? plz correct me.
The "volume" you're looking at is almost certainly TICK volume. In which case it would equal the selected tick size of the chart. It's NOT exactly the same thing as a constant volume chart. Although through some trial and error you can come up with a tick setting that, averaged over time, would approximate a particular constant volume chart.
For example say over a protracted period of time the average tick size of the underlying instrument you're charting is 10 contracts per tick. Generally speaking a
100 tick chart would roughly approximate a 1000 constant volume setting. Not perfectly but especially with larger settings in most cases you won't be able to tell much difference. Very small tick/volume settings on the other hand would tend to show bigger differences I should think.