Many people compared the Apple Watch Series 4 to the iPhone 4 while explaining the major design update Apple delivered this year. But Series 4 is perhaps more comparable to the iPhone 5S when it comes to processor technology. Just as the iPhone 5S was the first iPhone (and smartphone) to rock a 64-bit processor, the Apple Watch Series 4 happens to be the first Apple wearable to ship with a 64-bit chip inside.

We already know how much faster the S4 SiP (Silicon in Package) inside the Series 4 is, but a new discovery reveals that the processor can deliver performance similar to the iPhone 6s.

Apple says that the 64-bit dual-core S4 chip is up to two times faster than the S3 chip powering the Series 3. Over the weekend we saw a video comparison of the five Apple Watch models Apple released to date — the count starts at Series 0 — which shows exactly how fast the Apple Watch Series 4 is compared to every other model.

The Series 4 was the fastest, but the differences were not huge between Series 4 and Series 3, per MacRumors. But when comparing the new Watch to Series 2 and older models, you could really see the difference.

“If you’re considering upgrading from a Series 2 or earlier to the Series 4, do it. The speed changes are so drastic that using the Apple Watch Series 4 is an entirely different experience than using an older Apple Watch,” MacRumors wrote. But that speed comparison isn’t enough to showcase what the S4 chip can do, so well-known developer Steve Troughton-Smith came up with the following test:

Ok we may not have an Apple Watch benchmark, but holy shit I can do 60fps physically-based Metal rendering and realtime physics on the Series 4 😱 pic.twitter.com/GXza08pgIP — Steve Troughton-Smith (@stroughtonsmith) October 2, 2018

Apparently, the S4 can do “60fps physically-based Metal rendering and real-time physics,” using just 64% of the chip’s power.

*and* the CPU has headroom to spare. What a beastly CPU. I need an iPhone 6s or newer to get similar performance out of an iPhone with this app and this scene pic.twitter.com/5BW1gd0sWk — Steve Troughton-Smith (@stroughtonsmith) October 2, 2018

Here’s the same animation again in full screen:

As you can see, the S4’s power is impressive. For one thing, it shows Apple is future-proofing the Watch to better deal with whatever new feature it cooks up for future watchOS releases. But more importantly, the 64-bit S4 chip may be a stepping stone towards the processor that will power Apple’s rumored AR glasses. That chip will have to be just as small as the S4, if not even smaller, and power AR experiences far more resource-demanding than Watch apps.