Each line is a Tone’s output to an effects unit, and the circles with arrows are attenuators setting the send levels to the three effects units.
Here Part 1’s Output Assign is set to PATCH, so each Tone’s own send levels are used, while the Part’s send levels still scale its Patch overall.
Diagram from the XP-80 Owner’s Manual, © 1996 Roland Corporation, reproduced for educational purposes. Credits & disclaimer.