This small project is a drop chance calculator for the various drop formats of metin2 since the calculation itself isn't as straight forward as the format would suggest.
All the values are pulled from the leaked source and should also be correct for older versions.
The double drop item is set when an item of UNIQUE_GROUP_DOUBLE_ITEM is equipped.
The exact items may vary for you, they are all items in the special_item_group with vnum 10002.
There is a 0.002% chance for an additional 1000% increase in drop chance and a 0.01% chance for an additional 500% increase. I have ignored them in this calculation.
The chance will get triggered - on average - every 50.000 or 10.000 (respectively) mob kills, highly unlikely.