When using a finger or a stylus, the iPhone 6s or 6s Plus is able to detect 256 levels of pressure being on the screen, letting users draw thinner or thicker lines based on the amount of pressure that's applied.
For those unfamiliar with the Astropad line of apps, they're able to transform an iPhone or an iPad into a professional graphics tablet that can be used with the Mac by mirroring the Mac's display to the iPhone. The iPhone's touch controls are then used for creative tasks like editing photos and creating art with little to no lag. Because the app simply mirrors what's on the Mac's screen, it's compatible with any Mac-based editing app like Photoshop CC and Pixelmator.
The Astropad Mini app for the iPhone is now a free download, as is the Mac app, so the Astropad system can be used by anyone at no cost. The Mac app is available from the Astropad website and the iPhone app is available from the iOS App Store. [Direct Link]