If we configure a negative multiplier on a numeric (unsigned) item, we always get the same value: 18.45E.

The same works great with numeric float item.

The issue I have is that I want to graph both incoming and outgoing network traffic on the same graph, so I use a negative multiplier for the outgoing, so the graph will be reversed.

Until now, I used float item for traffic accounting (and the negative multiplier for outgoing), but, I hit bug ZBX-2272 (Item server02:net.if.in[eth0,bytes]] error: Type of received value [1264329667796] is not suitable for value type [Numeric (float)].
So, I tried to convert all these items to unsigned, but outgoing traffic doesn't work anymore with the negative multiplier.