Unclear behavior of downstream / upstream quantity

[BigDanTheOne]

Hello! I'm new to frepple. Currently, I am having difficulty understanding how downstream and upstream operations work in a manufacturing order (MO). I would greatly appreciate some assistance with this matter.

I understand that:

• The "downstream operations" allows me to follow how a certain produced quantity is being consumed by other manufacturing and ultimately ends up in a sales order for an end item.
• The "upstream operations" allows me to trace where the consumes material came from that a sales order or manufacturing order.
• Quantity somehow reflect the pegging of materials flow between operations.

What I don't understand is how exactly
Take a look at the screenshots:

Here we have MO 5 and 18. MO 5 produces multiple items, part of them are passed into MO 18.
Inside "downstream operations" of MO 5 it is written that 2/2 of something 2/2 of something else are passed into MO 18
Inside "downstream operations" of MO 18 it is written that 2/2 of something and 2/2 of something else are received in MO 18

My questions are:

1. What are this something that are passed into MO? Items? If Items than how can I understand what specific items are being passed?
2. Why do I have a situation where something that are passed into MO are not equal to something that are received?

[BigDanTheOne]

@jdetaeye Hello! I'm sorry to bother you, but you're my last hope for understanding this. I would really appreciate your help.

[jdetaeye]

Here are 2 slides from our training material. It's a straightforward FIFO material allocation across all levels in the supply path. The upstream&downstream operations just follow this material flow.