You can create a "Ratio" SharpChart where the main charting area contains the ratio of one stock divided by another by entering the first symbol, a colon character, and the second symbol inside the "Enter Ticker" box. For example, "IBM:$SPX" charts the ratio of IBM divided by the S&P 500. Ratio charts are best viewed with the "Line (NAV)" style setting. Example.

For more description on the calculation for ratio charts please refer to this Mailbag article and this video.