You can achieve this by adding another @State variable to store the interpretation text and updating it inside your button's action. Here's how you can modify your code:

@State var interpretation: String = ""  // New state variable for interpretation

Button {
    // Ensure all inputs are valid numbers
    if let setVT = Double(SetVT), let pplat = Double(Pplat),
       let lPEEP = Double(LPEEP), let hPEEP = Double(HPEEP),
       let vtTotal = Double(VTtotal), let vtHPEEP = Double(VTHPEEP) {

        let Cbaby = setVT / (pplat - lPEEP)
        let pVrec = hPEEP - lPEEP
        let ppVrec = pVrec * Cbaby
        let Vrec = vtTotal - vtHPEEP - ppVrec
        let Crec = Vrec / (hPEEP - lPEEP)
        let raw = max(Crec / Cbaby, 0)

        answer = String(format: "%.2f", raw)

        // Interpretation logic
        interpretation = raw < 0.5 ? "XXX" : "YYY"
    } else {
        answer = "Invalid input"
        interpretation = ""
    }
} label: {
    Text("Calculate")
        .fontWeight(.bold)
        .frame(width: 200.0, height: 50)
        .background(Color.blue)
        .cornerRadius(10)
        .foregroundColor(.white)
        .font(.system(size: 20))
        .padding()
}

// Display result and interpretation
Text("RI = \(answer)")
    .font(.system(size: 20))
    .fontWeight(.bold)

Text(interpretation)
    .font(.system(size: 18))
    .foregroundColor(.gray)

Explanation:

1. Added @State var interpretation: String = "" to store the interpretation.
2. Used a conditional (raw < 0.5 ? "XXX" : "YYY") to assign the appropriate interpretation.
3. Handled invalid input cases to prevent crashes when the user enters non-numeric values.

Now, when the user clicks the button, the calculated result will be displayed along with a meaningful interpretation!