Any of the icons on the System Stability Chart can be selected to move the scope of the System Stability Report to a specific time period. This is very useful because it allows you to see what happened the same day or just before some kind of failure occurred. Depending on this information, you will have a clue as to what may have been the cause of the failure.
Reading the System Stability Report
Every day your computer is given a System Stability Index rating based on the system activities of the day. The score is out of a possible 10 points. Depending on what has happened in the past, this score goes up or down. For example, if you have a Windows failure, your score goes down. As days pass, if you do not have any more failures, your score gradually goes back up again. However, if another failure occurs, it drops even more.
I recently had an issue with installing new video drivers for my laptop. I was trying to get the Aero Glass look in Windows 7 to work and was installing some drivers that were not exactly made for my laptop model. After I installed the new drivers, I had to reboot and was welcomed by the blue screen error. I rebooted again and the same thing happened. These system failures killed my System Stability Index. Before I had these problems I had a rating of 9.44; after my driver fiasco, I had an index of 4.711. As you can see, your reliability rating can drop very quickly if you have multiple major errors, such as a blue screen.
When you notice that your System Stability Index goes down, you are going to want to know why, so that you can fix the problem and get the performance of your system back in line. The System Stability Report is perfect for understanding exactly what happened.
With your mouse, select a time period on the System Stability Chart in which your score dropped significantly. Depending on presence of the information, warning, or error icons in the grid for the specific day, you will know what sections of the report you should expand to see the details of what happened. The red error icon in the Application Failures grid item on the selected day tells you to expand the Application Failures section of the report to see the details. After expanding the section, you will see which application failed and how it failed. Similarly, if this were a hardware failure, you would see the component type, device name, and why it failed. If it were a Windows or miscellaneous failure, you would see the failure type and details of what happened. As you can see, reading the System Stability Report is a quick and easy way to see what exactly is going on.
Source of Information : Windows 7 Tweaks 2010