The Withings Health Mate™ app is compatible with the following list of iOS devices, provided they run iOS 7 or higher:
- iPhone 4 or higher
- iPad 2nd Gen or higher
- iPad Mini (all generations)
- iPod Touch 3rd Gen or higher
While there isn't a fully optimized version for the iPad, you can still install the iPhone app on your iPad. Besides possible display issues, the only limitation is that you won't be able to measure your heart rate using the camera.
If your device is running iOS 6 (if you have an iPhone 3GS, for example), you still have the option of installing the app, although you won't be able to get the latest versions and enjoy all the new features.
To do so, you need to download the Withings Health Mate™ app on iTunes from your computer. You can then go to App Store > Updates > Purchases on your device and download a compatible version.