Musketeer and Pikeman slots . . .?

[Exile]

How do they function?

I know that these slots, given that the numbers are correct, will obsolete everything to their left?

How does this work?

Mathematics, etc.

[EZRhino]

IRC, the effect is player specific and is triggered by having the aforementioned units actually under your control, rather than researching a technology. Any one movement unit with lower defense than Musketeers becomes obsolete. Ditto for double moment units vis a vis whatever is in the Knight's slot. I believe the barbarians are unaffected by the obsolescence effect