MK: A Problem With Equity Charts

Hi Matthew,

I posted this on another thread, but thought I’d bring it to your attention in case you missed it:

"Have you ever zoomed in on a chart and noticed how the equity balance on the LH scale declines as you zoom in (often by 40% or more!) Probably just a scaling issue, but it hardly encourages confidence that what you’re viewing is accurate. This happens with both IE and Firefox."



I’m not really sure I understand what you mean. Perhaps you can email me specific screenshots / pictures?


Let’s take an example, and [LINKSYSTEM_26068544]!

Look at Have Fun’s chart, in Apr 2008 you’ll see it went through a “flat period” with a low near $148,000 balance on the LH scale. That low is hit on 04/25/08.

Now zoom in on that date, and continue until the red bar in the zoom “ladder” is at the 4th highest rung. (The “ladder” that appears to the right of “Click on chart to zoom and center” once you start zooming).

What I see at that point is a balance on the LH scale for 04/25/08 of around $98,500 … a long way from $148,000!

Does anyone else see the same behavior?




The Have Fun system has over 16 months worth of equity data. In your example above, you say that when you look at the original chart, you can pick out the exact date of a low equity point (4/25) from that little chart.

But I would posit that, with such a large amount of data, and such a imprecise graphical granularity, determining the low date from the initial chart is pretty near impossible, without an error of at least, say +/- 1 month. When I start zooming in on the chart by clicking it, though, it becomes easier to see month-by-month (and then week-by-week) changes. And then the chart’s ups and downs seem very consistent to me from one zoom to the next.

It really has to be consistent; the charts are drawn dynamically using the same data set. It’s unlikely I found a way to mess that up.

The "problem" is that the chart will always start with $100K at the left side, regardless of the selected time period. So it is not really an enlargement of the total chart. Suppose that the system has $500K at day X and $600K at day X + 30. When you zoom in at that period you will see the equity go from $100K to $120K, not from $500K to $600K.

The advantage of this is that it shows how your equity would develop if started trading with $100K at day X. The disadvantage is that it is not really a pictorial zoom (as some would expect) but rather a trading zoom.

Yes, good point. I actually meant that to be a feature, not a design flaw.

Aahhh, thank you Jules!

Now I understand: it’s effectively being indexed to the start of whatever period you’re looking at with the current zoom level. Except the original, un-zoomed chart.

Very clever and probably better than non-indexing (especially when system comparisons are being done). But perhaps a gray box popping up to explain the behavior would help? Or did I miss that too?

- Murray