How to tell if current running Apple Watch size/dimension is 38mm or 42mm?

We know that there are two screen sizes for Apple Watch: 38mm and 42mm. The WKInterfaceDevice class provides a readable property named screenBounds. I wrote an extension for WKInterfaceDevice, trying to add a method to detect current device type.

import WatchKit

enum WatchResolution {

    case Watch38mm, Watch42mm
}

extension WKInterfaceDevice {

    class func currentResolution() -> WatchResolution {

        let watch38mmRect = CGRectMake(0.0, 0.0, 136.0, 170.0)
        let watch42mmRect = CGRectMake(0.0, 0.0, 156.0, 195.0)

        let currentBounds = WKInterfaceDevice.currentDevice().screenBounds

        if CGRectEqualToRect(currentBounds, watch38mmRect) {

            return WatchResolution.Watch38mm
        } else {

            return WatchResolution.Watch42mm
        }
    }
}

Is that the correct method to detect Apple Watch size? Is there another method I am missing in the Apple docs?

This is what I am doing:

enum WatchModel {
    case w38, w40, w42, w44, unknown
}

extension WKInterfaceDevice {

    static var currentWatchModel: WatchModel {
        switch WKInterfaceDevice.current().screenBounds.size {
        case CGSize(width: 136, height: 170):
            return .w38
        case CGSize(width: 162, height: 197):
            return .w40
        case CGSize(width: 156, height: 195):
            return .w42
        case CGSize(width: 184, height: 224):
            return .w44
        default:
            return .unknown
    }
  }
}