PerfCharts Performance Value For A Given Date Changes Simply by Moving the Date Range Slider

sales13

Hello,

I have noticed an anomaly in the PerfChart of StockCharts.com.

I am attaching two screenshots in SPY Perf.zip (not able to attach more than one screenshot so had to zip them) that illustrate this:

* SPY Perf 02-15-2019.png - Shows the 252 day performance of SPY on 01/31/2019 to be +2.03%. This was captured today with the hard right edge of the chart = 02/14/2019.

* SPY Perf 01-31-2019.png - Shows the 252 day performance of SPY on 01/31/2019 to be -2.43%. This was also captured today with the hard edge edge of the chart = 01/31/2019, and was what I saw around 01/31/2019.

By just scrolling the 252 day (or any other period) date range to reflect a different hard right edge, the performance can greatly change. I am not understanding why a past performance value would change in this way - shouldn't these be fixed throughout time?

Can anyone help clarify this behavior?

markd

Notice that the left edge - the start date - changes, too. So, the value for 1/31 on the 2/14/18 - 2/14/19 is not derived from the values 252 days apart - 1/31/18 and 1/31/19 - it's the value derived from the values of the instrument on 2/14/18 and 1/31/19.

So, in other words, all values are derived from the instrument's value on the start date and the end date (or selected intermediate date). That's why the perf line always begins on the zero line no matter what start date you choose.