I am trying to understand how data are compared in "Comparison Overly" chart. If I want to compare, say, XLU to SPY using Comparison Overlay, two lines are drawn in the same chart. On the Y axis it shows XLU price, but what does SPY line mean in the chart? Are these two lines drawn based on their percentage changes, using a common starting time (1st bar in the chart) as a reference point? In other words, how data in comparison overlay chart are calculated? Thanks very much in advance.

If you have Start All Plots at the Same Point checked in the Comparison Overlays window then yes, things all start at the same point on the left edge of the chart. Percent changes are calculated at each bar with the result being converting into the scale being used by the main symbol on the chart.

Comparing Price Plots Visually (4:13)

Since it is price percentage change comparison, using left edge first bar in the screen as a reference point, is it possible to see the actual percentage change values on the right Y axis, instead of showing the current price absolute close value?

Fo example I wan to compare US major industry sector peformance (% change) since year start, and I woud like to see each sector's % change on Y axis. Is this possible? Thanks.

You can click on the ruler near the bottom of the scale and make sure % is selected to view percentages.

Ruler Scale (2:57)

I tried to put CPC-X and CPCE-X on the same price chart with the same horizontal reference line(s), say 1.0. I made CPC-X as the primary symbol and CPCE-X as the comparison symbol. My problem is I could not get CPCE-X scaled to CPC-X for the same reference lines. Any suggestions? 

Thanks!

You might want to try adding the CBOE Equity Put Call Volume Ratio to the chart as its own symbol instead of as a comparison overlay.

Click on the CPC-X plot and select Add Plot Here. Then choose CPCE-X - CBOE Equity Put Call Volume Ratio from the Indexes tab. Choose Scale with CPC-X CBOE Put Call Volume Ratio when prompted (not "by itself").

Excellent and thanks for the detailed instructions. It is exactly what I need. :)

You're welcome.