People keep saying there is some embedded scaling for groups of monsters but I am not seeing it. As far as I can tell, 1 CR = 2, 2 CR 1s = 4, 3 CR 1s = 6. Its a linear progression, there is no adjustment for groups that I can see.
People are saying this one tends to require more monsters for equivalent challenge compared to the base system, to which I respond....yes!! Once you hit 5th PCs are ridiculously hard to kill, I think all of the standard encounters are over CRed in base.
If you follow the DMG encounter building system, you get 2 CR1s is roughly a CR3, not a CR2.
The OP (and I) deconstructed the DMG XP system and we think we found a different scale than CR. In that scale
you can just add.
The big differences is the CR 0 to 3 range.
CR 1/8 is 1/6 of a point
CR 1/4 is 1/3 of a point
CR 1/2 is 2/3 of a point
CR 1 is 1 point
CR 2 is 1.5 points
CR 3 is 2 points
After that, from 4 through 15 or so, you get 1 point per CR. I and the OP disagree how to best fit in a relatively unimportant way.
From 15 to 20 we reach 23ish points. After 20, we get like 5 points per CR.
In this "point" system, adding works.
The difference is that addinc CR will have 5 CR 3 monsters be CR 15, but adding points makes them CR 10ish.
For CR 1 monsters, the results are similar after the first 4 or so (CR will disagree by 1 or so).
For sub-1 CR monsters, there is lots of divergence; adding CRs will result in lower total CR than using points/the DMG guidelines.