I have a question, which looks silly but I am getting different opinion among our stake holders. I need to report an improved performance in our new version of software, where the total time required for for a functionality, say 'Login' in new version takes 2 seconds where as it takes 4 seconds in our previous version.
Now, how do I present this in terms of percentage improvement in performance? Is it ((2-4)/2 * 100 = 100% gain) or (4-2/4 * 100 = 50% gain in terms of time saved) ?
Pls note : This is comparison of same software between two versions and not b/w two different products. So, is there any rule on which one should go to denominator?.