Odds for “/r 2d100” vs “/r 1d100=1d100”

We are playing a custom rpg on roll 20 based on Jujutsu Kaisen and using its chat feature. The rules for this state “When someone makes a physical attack using cursed energy, the DM rolls 2d100 in secret. If both dies roll the same number, a Black Flash occurs.” Our DM has told me that the intention is that the chances of a Black Flash occurring is 1/100, but the way they roll shows to me that it results in a 1/10,000 chance. I suspected that rolling “1d100=1d100” would result in the intended 1/100 chance, but I’m not sure. Can someone please explain to me a command that would allow for the 2 dice being the same to lead to a chance of 1/100?

Upon further consideration, I guess what I need to know is if rolling “1d100=1d100” is dependent or independent

If the roll is two d100, and you compare them both to see if you have a match, the chance is indeed 1/100. If you want to find the chances of these, roll20 isnt a good place. You'd be bette rof using something like anydice.com. We'd have to see the text of the macro your GM is using to know if it was working correctly.

When rolling 1d100 = 1d100: the result is dependent on both dice, but each d100 roll is independent. The odds for /r 2d100 cannot be described easily. There is a 1 in 10,000 chance of each exact result, but some numbers on the roll occur more than others since you can roll 100 in more ways than 200..

The macro the GM uses is “/r 2d100” if that helps

how do they test for matches? When rolling 2d100, Roll20 shows you both dice, so the GM can look to see if they are equal. That will give 1/100. There is also an mt operator which will show if the dice show the same value. Here's an example with a much smaller dice to show what happens when you get equal results: I suggest your GM should be rolling /r 2d100mt

If your GM simply wants to see a result that displays when two dice match, then they can use the ' Dice Matching ' argument in a roll. You can test this out with a smaller roll: /roll 2d4mt1 or [[2d4mt1]] For the /roll command you'll see red lines over the two numbers if they are matching and a "1 Match" message.  For the inline roll using 'mt' you'll get an output of 0 if they don't match, and an output of 1 if they do match, and you can hover over the result to see what numbers were rolled. Change those to /roll 2d100m1 or [[2d100mt1]] for matching two d100 dice rolls.

Regarding odds lets simplify things:  1d3=1d3 vs 2d3 1 1 1 2 1 3 2 1 2 2 2 3 3 1 3 2 3 3 Whether the roll is 2d3, 1d3=1d3 (which checks for one roll equalling the other roll) or 2d3mt the odds are the same.  2d3: the GM mentally verifies if there is a 1 1, a 2 2, or a 3 3.  1d3=1d3: Roll20 verifies if the two rolls equal each other (match) and then that is a success.  2d3mt: Roll20 states whether two rolls match.  Three different ways to do it, same result.  1d100 is no different. Whether the GM uses 2d100, 1d100=1d100, or 2d100mt the odds of matching rolls are the same. 

Since it's a secret roll, your GM might prefer /w GM &{template:default} {{match=[[2d100mt]]}} This will send a message of match 1 if there's a tie, and match 0 if there isn't, and the GM can hover over the 0 or 1 to see the dice rolls. It's more compact and will take up a lot less of their chat log.