Pokémon Go is more than it seems. The phenomenon has truly unique and innovative gameplay, but it didn’t seem to have a ton of depth to it—especially since the battle system is relatively curtailed (for now). Well, it turns out we’re wrong. Like the handheld Pokémon game, Pokémon Go is more complex than it looks. That’s because every Pokémon actually has secret stats that determine its growth, how it levels up over time. It’s not just random. That’s right: Pokémon Go has IV’s.

Pokémon Go Stats: The Secret Numbers That Make Your Pokémon Tick

IV’s, short for individual values, are hidden numbers attached to every Pokémon. They’ve been around in the regular Pokémon games for years, and the enterprising Redditors of r/TheSilphRoad have discovered that the same stats exist in Pokémon Go and are visible in the game’s code. The details are complicated, so take a look. Here’s the gist: Every Pokémon has invisible stats that determine their attack, defense and stamina. This is independent of the Pokémon’s CP. So two Pokémon with the same CP could fight very differently. It’s unclear how or whether this relates to the Pokémon’s HP or Weight, but it affects how their stats change both as they evolve and as you use Stardust to power them up.

Like in the regular Pokémon games, IVs in Pokémon Go can be a little tricky to calculate. They’re meant to be an invisible value, one that most gamers will never see. If you’re just a casual player, you don’t have to care all that much. But if you want to be a serious Gym competitor, or a serious trainer-to-trainer competitor if and when direct combat gets rolled out, you’ll need to know about IVs.

Luckily, there are already online IV calculators. Here’s one, and another. Both will help you calculate which of two Pokémon of the same species is stronger, although it takes a fair amount of legwork and a bit of Stardust on your part to make it happen. The key takeaway on your part: Not all Pokémon are created equal. Beyond the question of whether to power up a Pokémon before or after evolving one, IVs can determine whether a Pokémon with slightly lower CP actually has more long-term potential. The full implications, not to mention the mechanics underlying the game, haven’t been sussed out yet. But here’s what we do know: There’s more to winning at Pokémon Go than we first thought… and the game is much more complicated than it appears on the surface.