Kind of in line with the other posts'
There are two types of relative strength that should be considered.
1) Price performance between two product's i.e. stock price to an index, SPX, Sector, another stock( i.e. INTC/AMD).
2) Absolute relative strength - stock price to itself x periods ago.
Absolut relative strength can be calculated in a multitude of way's. One being currently weekly close divided bye the weekly close 26 weeks ago. (Used by Levy and Kirkpatrick). Another use of absolute relative strength is used by IBD where it's a combined version of absolute strengths. RS = (20* (2*C/C63+C/C126+C/C189+C/C252-5).(Where C is the current close price today and C63 is the close 63 day's ago, etc for the others.
Both would be extremely helpful, as an indicator and a unisort, ranking could there by be achieved. Also being able to set the day's as a variable would be helpful and product selection to compare would be as well.