In your completed Production Control Model,$$

Add $+/-$ signs on all the arrows

Find the loop$($s$)$ responsible for the oscillatory behaviors in the system.$$

Mark the loop$($s$)$ by changing the color of the arrow $($ex$.$ green, red, etc.$)$ and label the loop$($s$)$ with B$/$R sign$($s$)$ with the same colored font.$$

If you have more than one loop, make sure the loops are marked with different colors.