I'm trying to learn a bit about routing high-speed differential signals. One thing that is confusing me is that often schematics talk about routing certain signal pairs with a specific impedance (usually 90 or 100Ohms). Though while reading into the topic there seems to be quite few different ways to calculate impedance depending on how the signal is propagating through the traces. I'm presented with odd, even, common and differential impedance and when I want to calculate a specific impedance for a microstrip with this tool, it gives me the impedance for all four types mentioned before.
How do I know what the schematic is referring to? Differential impedance sounds obvious but it seems to be a very complicated topic so I don't want to jump to false conclusions.