diff --git a/README.md b/README.md
index 613b611..08d4aa4 100644
--- a/README.md
+++ b/README.md
@@ -4,4 +4,7 @@ Kalkulator BMI
 Silahkan kembangkan aplikasi ini untuk melakukan perhitungan BMI
 
 Petunjuk lebih detil dapat dibaca di
-https://docs.google.com/document/d/1iGiC0Bg3Bdcd2Maq45TYkCDUkZ5Ql51E/edit?rtpof=true
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+https://docs.google.com/document/d/1iGiC0Bg3Bdcd2Maq45TYkCDUkZ5Ql51E/edit?rtpof=true
+
+Starter dimodifikasi dan terinspirasi dari:
+https://developer.android.com/codelabs/basic-android-compose-calculate-tip#0
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diff --git a/app/src/main/java/com/example/tiptime/MainActivity.kt b/app/src/main/java/com/example/tiptime/MainActivity.kt
index d0fdd80..4a0edce 100644
--- a/app/src/main/java/com/example/tiptime/MainActivity.kt
+++ b/app/src/main/java/com/example/tiptime/MainActivity.kt
@@ -127,11 +127,11 @@ fun TipTimeLayout() {
             modifier = Modifier.padding(bottom = 32.dp)
         )
         Text(
-            text = stringResource(R.string.bmi_calculation, bmi),
+            text = stringResource(R.string.bmi_calculation, bmi), // rumus
             style = MaterialTheme.typography.displaySmall
         )
         Text(
-            text = stringResource(R.string.bmi_category, category),
+            text = stringResource(R.string.bmi_category, category), // kategori
             style = MaterialTheme.typography.displaySmall
         )
 
@@ -185,13 +185,22 @@ fun RoundTheTipRow(
  *
  * Catatan: tambahkan unit test untuk kalkulasi BMI ini
  */
-private fun calculateBMI(BmiHeight: Double, BmiWeight: Double = 15.0, roundUp: Boolean): String {
-    var bmi = BmiWeight / 100 * BmiHeight
-    if (roundUp) {
-        bmi = kotlin.math.ceil(bmi)
+private fun calculateBMI(BmiHeight: Double, BmiWeight: Double, useUSC: Boolean): String {
+    if (BmiHeight <= 0 || BmiWeight <= 0) return "0.0"
+
+    val bmi = if (useUSC) {
+        // USC: Berat dalam lbs, tinggi dalam inches
+        703 * (BmiWeight*2.2) / ((BmiHeight*0.29) * (BmiHeight*0.29))
+    } else {
+        // SI Metric: konversi cm ke meter
+        val heightInMeter = BmiHeight / 100
+        BmiWeight / (heightInMeter * heightInMeter)
     }
-    return NumberFormat.getNumberInstance().format(bmi)
+
+    return String.format("%.2f", bmi)
 }
+
+
 /**
  * Calculates the BMI Category
  *