Hello! I tried to stress-test my system and task manager reported the following: Tuneup Process Manager says differently: Now what to think? Just a Windows 8.1 bug or a problem with my system?!
The 2 programs don't take reading samples at the exact same time. This is why the 2 graphs have a bit different shape. They are similar, however, so there is no bug here. Launch 10 monitoring software at the same time and you'll have 10 different, but similar graphs.
One by one != at the same exact time. As eydee said, it takes samples at different execution time, and to have more similar graph you would have to launch the monitoring to start down the same nanosecond (virtually possible, but who does it?), but even then, software time will still be slightly different, because the monitoring software itself is also executed and is taking execution time, and it's time is displayed only on next sample read. If you need a 100% reliable timing on the graph reading, you connect an oscilloscope to the motherboard, configure it to operate at the same exact Hz as the CPU (make sure to disable power-saving features that can lover the rate, or the reading will be wrong), and take samples graph on it. But only very specific category of people need that big preciseness on their graphs (mostly electronic engineers).
The 2nd pic's valley in between the peaks is exaggerated. Some programs don't graph things exactly the same way; or interpret them the same way for that matter. While the first tool probably more accurately represents the cpu-load, the 2nd one exaggerates the time when it's at 60% load. I'm sure it does this because it separates them by color.