How to make the Ubuntu Linux 16.10 System Monitor % CPU utilization agree with ps or top for a Firefox process on quad core CPU?

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 https://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?