Hello Eric, I apologize for the long delay in my response, I want to see the index because in my stock Dataset I have a field called "Index". My algorithms use that index and when something goes wrong (or seems to go wrong) with the calculations I debug my code and see what the index is. I then would like to see which candlestick I am dealing with. That task would be made so much easier if, as I move the mouse over the candlesticks, I could see not only the Date and O,H,L,C but if I also see the index. But so, far, no one has suggested a solution.

It seems to me like TradingChart is very hard-coded in terms of its display. I wasn't able to add labels or tooltips, and I couldn't find any option like DisplayFormat or something that would allow me to provide my own display function. There is an option called EventLabels, but I wasn't able to get it to do anything dynamically. I think if you created an event label for every date, it would be too cluttered to be useful. The next thing I would try is to look at FullForm[TradingChart[...]] and try to find where the mouseover display is happening. Maybe you could just directly replace that for testing purposes.

Thank you for offering help Eric. Let me be a bit clearer.

1) Yes, I use explicit FinancialData of the form {{#Date, {#Open, #High, #Low, #Close, #Volume}}}. using the following code

makeChart[currentCandles_Dataset] := 
  TradingChart[{#Date, {#Open, #High, #Low, #Close, #Volume}} & /@ 
    currentCandles];

where I have a Dataset called currentCandles which, among other things, contains the Date,Open,High,Low,Close and Volume of each candle.

At the moment, if I display a TradingChart or an InteractiveTradingChart, the information at the top of the charts is O,H,L,C and Date of the candle currently under the cursor.

My application provides information such as "There is a peak at bar #6" or "A trendline was broken at bar #23". So, when I want to visualize if the output of my algorithm is correct, I use the TradingChart and I try to go to bar #N rather than go to bar on Tuesday, December 4.

It would be easier for me to zoom in on a bar quickly if I simply could see the index of the bar (meaning its index in the Dataset). That is why I would love to be able to add a string like "I: N" at the front of the information currently being presented by the TradingChart.

Is this clearer? Thank you for any help.

I haven't been able to figure out a way to do this yet. But maybe we can come up with a workaround. Are you building your TradingChart from explicit data (e.g. FinancialData)? Can you clarify what you mean by "an application that refers to the candlesticks by their indices"? Do you mean you want something to work programmatically, or do you just want to see the indices so that you can visually compare two different representations? Or do you mean something else entirely?