Talk:Mercurial Scimitar/@comment-84.109.94.152-20121117125330/@comment-4834593-20121119203430

It actually calculates from the total of all your flat movement speed, so base movement speed + boots + buffs like Singed ult and Sona's E persistent effect.

About the diminishing effect, from 400 to 500, it's 90% as effective, after that, only 50%. The same on the other side, below 220, all slows are 50% as effective, making it impossible to get below 110 movement speed.