Markup . . .
-- I buy a cabbage for $1.00 and put it on the shelf in my store.
-- I mark it up 100% . . . I offer it for sale for $2.00
-- I mark it up 200% . . . I offer it for sale for $3.00 .
Markdown . . .
-- I buy a cabbage for $1.00 and put it on the shelf in my store.
-- I mark it down 100% . . . I sell it for zero. (I give it away.)
-- I mark it down 200% . . . I give you $1.00 to take it home with you.