Adding to this, btc prices are measured only by their market price. So in the present situation, being as volatile as btc is,a merchant would have to have a floating value based on the market instead of a fixed price which makes it much harder for traditional or smaller merchants to accept btc.
I'm replying to your post since this is in fact my post that got copy-pasted by the dude you replied to
I have explained this issue a few times already. This is a sort of vicious circle or an evil feedback loop (you choose which). The price is volatile (and will remain volatile) because merchants and vendors are not accepting Bitcoin for real, i.e. they don't accept real bitcoins but are looking for fiat only as I made clear in my post, but they are not accepting it because its value fluctuates too much to make any real commerce possible. So we are basically stuck. Personally, I don't know of a viable solution how to break this self-sustaining loop of volatility, but others may have a different view or take on this situation and how to solve it