For those of you who have been using simulators for a while, you have probably seen terms like "error target" and "iterations" used, and they generally impact how "accurate" your simulation will be and how long it will run. But most people aren't that clear on exactly what these mean and what they should care about. Here we explain!
WoW simulators work on a very basic principle: the game is too complex to come up with a mathematical formula to calculate how much DPS a given player will do, so we create a model of the game that is as close to the real thing as possible, but waaaay faster. Then we simulate e.g. 1000 fights in a few seconds, and average the DPS from all 1000 of those. This average DPS is what you can expect to do on any given fight.
The number of fights that we average will determine how accurate that average is. A simple analogy would be measuring the length of a unicorn's horn: there are 1 million unicorns in the known universe. If we find 10 of them and measure their horns and average, it probably won't be a very good average. Maybe we found the 10 unicorns with the puniest horns. If we instead spend a bit more time and measure 1000 unicorn horns, the average will be much more likely to be accurate for any given unicorn.
We use an Error Target to figure out how many fights to simulate to get your average DPS. The idea is simple: I want to know my average DPS with a known amount of certainty, e.g. within 0.25% of the true average. I don't really care how many fights I need to simulate to get that accuracy, just stop once it is that accurate.
This is by far the best way to tell a simulator how long to run, and it is the only way to do it in the AMR simulator.
"Iterations" is simply another word for the number of fights to simulate. Back in the day, most people would run a fixed number of iterations, e.g. 10,000. The problem with this is that some specs take a lot more iterations than others to get the same amount of certainty -- their damage is prone to more randomness or big swings. So you really don't know how accurate your result will be if you run a fixed number of iterations.
We no longer display the number of iterations on the AMR simulator because it is a useless number. It is a terrible way to tell the simulator how long to run. You want to get a specific amount of accuracy, not a variable amount of accuracy.
Iterations are an implementation detail, not something that users of a simulator should care about. It was a mistake to ever make it something "visible" to the end user, and we are correcting that mistake.
If you want more accurate simulations, set a smaller Error Target! That will necessarily run more iterations behind the scenes, and it will stop once your target is reached. The margin of error is calculated via well-known statistical formulas -- there's no way to "cheat" it and reduce error with less iterations. Some specs will just take longer than others.