I would like to make the Ubuntu Linux 16.10 System Monitor % CPU utilization measurement basically agree with the `ps` "pcpu", % CPU utilization for an individual Firefox browser process running on a Lenovo Thinkstation desktop with quad cores.

The Ubuntu Linux 16.10 System Monitor Preferences are currently set at:

 Update interval in seconds: 3.00
 Enable smooth refresh: Yes
 Alert before ending or killing processes Yes
 Divide CPU usage by CPU count : Yes

 
The ps output for the Firefox process is:

 $ ps -eo pid,rss,c,pcpu,cputime,cmd | grep firefox
 2848 726024 3 3.5 00:50:23 /usr/lib/firefox/firefox -new-window

After reading http://unix.stackexchange.com/questions/67647/linux-see-cpu-usage-by-a-process-for-the-last-second, I learned how to view cpu usage for the last second. The top output for the Firefox process is:
 
 $ top -b -d 1 | grep -in "firefox"
 8: 2848 ratio 20 0 1980240 641516 115240 S 18.8 15.9 73:10.86 firefox


 For the Firefox browser app, I get 3.5% pcpu from `ps -eo pid,rss,c,pcpu,cputime,cmd` while for the same Firefox browser app, the GUI Application Ubuntu System Monitor shows 5% CPU utilization. In addition, I get 15.9% CPU usage from top -b -d 1 | grep -in "firefox". When that is divided by 4 for the 4 cores used by our CPU, I get 4.0% for top's output. 

 How can I get the `ps` or top outputs and System Monitor values to agree? Should I enable the Divide CPU usage by CPU count checkbox?


 [1]: http://unix.stackexchange.com/questions/67647/linux-see-cpu-usage-by-a-process-for-the-last-second?rq=1,