It's random.
So take your drop ratio (x:10,000) and calculated the Adjusted Drop Ratio.
Then a random number between 0 and 10,000 is rolled by the server and if
RandomValue <= AdjustedDropRatio
You receive the item.
For example, lets say you wanted to steal a Skull, with level 10 Steal and 100 DEX. The monster has 10 DEX. The skull drop chance is 10% (10% is a ratio of 1000:10,000)
AdjustedDropRatio = 1000 * (100 + 3*10 - 10 + 10)/ 100 = 1000 * (130)/100 = 1300
So your adjusted drop ratio is 1,300:10,000, meaning you have a 13% chance to Steal the skull.
A random number is taken by the server. If the random number is less than or equal to 1,300, you will receive the skull.
There is also a check to see if Steal is successful or not. Level 10 Steal has a 64% chance to steal, so there are two checks before an item is stolen.
If your steal attempt is unsuccessful, you will attempt to steal the next item.
Many monsters have extremely high drop items in their first slots (Common loots, typically 50%+ drop rate), making it fairly difficult to get rare items from a steal, since they are almost exclusively placed at the end of the list.
So lets say a monster drops these 7 items:
Skull (70%), Brigan (70%), Oridecon (30%), Elunium (30%), Chainmail (25%), Silk Robe (25%), Elemental Sword (0.02%).
If you wanted to Steal the Elemental Sword (Which would be extremely unlikely), you would have to do this:
Fail to Steal Skull, Brigan, Oridecon, Elunium, Chain Mail, AND Silk Robe, then successfully roll an extremely small number on the 7th roll.
If you considered the same stats from the first equation, Skull and Brigan would have a 91% steal chance, and your Elemental Sword would have a 0.02% steal chance, assuming you fail a 91% chance twice, then you failed two 39% chances, and then you failed two 32.5% chances.
So getting that Elemental Sword would be nothing short of a miracle.
tl;dr a roll is just another way to say random number.
How you know the DropRatio= % x 10,000?
Where did you find out about the role ( is it correct if I assume this= the "steal check"?)= random number?
So, the server'll calculate the "AdjustedDropRatio" for every item first, then make a role, then checks against the steal 64% chance to see if it succeeds, if not then check again the 64% steal chance for the following items, till the 7th monster drop item slot, if it succeeds then it will drop?
Also, basically, so the real steal chance for say the above skull you said= 0.91x0.64= 58.24% chance to succeed right?
If you wanted to Steal the Elemental Sword (Which would be extremely unlikely), you would have to do this:
Fail to Steal Skull, Brigan, Oridecon, Elunium, Chain Mail, AND Silk Robe, then successfully roll an extremely small number on the 7th roll.
Wait, so throughout a steal attempt, there's only 1 number the server randomly selected to compare with the adjusted rates right?
Is db.irowiki.org's monsters' drop slots' order accurate and read left to right and in a downwards fashion?