If you create a 500 Volume Bar chart, the bars aren't capped at 500. Their amount can vary from bar to bar, thus destroying the consistent value of the chart.
Interesting - I've never seen that before. Only the last bar of the day is not the proper volume size which I attibute to the fact that they seem to "reset" things at midnight.
How I see it is that if you are building 500 share bars and right now you are at 490 and a 50 share trade goes across then the bar wil go up to 540, close, then start the next bar. Hard to get around.
That is exactly how eSignal built their bars the last time I checked and it is an easy fix. MultiCharts, Ensign and Sierra all take the eSignal feed and correctly build the Volume Bars by capping the volume to a user defined amount. If they can do it with with the esignal feed then eSignal should be able to do it . . . especially when MultiCharts does a bulk of eSignal's programming. It is simply a matter of priorities. That same scenario done correctly would have 10 of those shares being attributed to the bar with 490 and the balance of 40 shares going to begin the next bar.
Based on the following link Esignal is properly constructing constant volume bars: "...For example, to create a 1000 contracts per bar bar chart (meaning you want the bar to fill with 1000 contracts or shares before starting a new bar ) you will have to enter 1000V. For any number of shares traded higher than the specified interval, the trade will be split among multiple Volume Bars." http://kb.esignalcentral.com/display/2/articleDirect/index.asp?aid=1275&r=0.597851
The link is dead and according to eSignal Support their Volume Bars aren't capped to the user specified amount. If this problem has been fixed then let someone from eSignal post a comment here saying so.
Tradestation is even worse. They know about the problem, they were contacted but one of their most affluential customers and told about it, their tech support tried to get my programmer to give them his code that fixed it but refused to fix it on their own saying it was a waste of time that no one cared. That is shear arrogance.