diff --git a/app/src/main/java/eu/wa5p/lightmeter/MainActivity.kt b/app/src/main/java/eu/wa5p/lightmeter/MainActivity.kt
index 69bc4d7..dd39bab 100644
--- a/app/src/main/java/eu/wa5p/lightmeter/MainActivity.kt
+++ b/app/src/main/java/eu/wa5p/lightmeter/MainActivity.kt
@@ -48,7 +48,10 @@ class MainActivity : ComponentActivity(), SensorEventListener {
         enableEdgeToEdge()
         setContent {
             LightMeterTheme {
-                LightmeterHomeScreen(state = lightmeterState )
+                LightmeterHomeScreen(
+                    state = lightmeterState,
+                    recalculateShutterSpeed = { recalculateShutterSpeed() }
+                )
             }
         }
 
@@ -56,18 +59,25 @@ class MainActivity : ComponentActivity(), SensorEventListener {
         illuminanceSensor = sensorManager.getDefaultSensor(Sensor.TYPE_LIGHT)
     }
 
-    private fun updateLightmeterState(illuminance: Double) {
+    private fun recalculateShutterSpeed() {
+        val illuminance = lightmeterState.value.illuminance
         val iso = lightmeterState.value.iso
         val aperture = lightmeterState.value.aperture
         val shutterSpeed = (aperture * aperture) / (illuminance * (iso / 100))
         lightmeterState.value = lightmeterState.value.copy(
-            illuminance = illuminance,
             iso = iso,
             aperture = aperture,
             shutterSpeed = shutterSpeed
         )
     }
 
+    private fun updateLightmeterState(illuminance: Double) {
+        lightmeterState.value = lightmeterState.value.copy(
+            illuminance = illuminance
+        )
+        recalculateShutterSpeed()
+    }
+
     override fun onSensorChanged(event: SensorEvent?) {
         event?.values?.let {
             for (v in it) {
@@ -138,9 +148,8 @@ fun LightmeterListItemPreview() {
     }
 }
 
-// TODO: Recalculate state on change
 @Composable
-fun IsoSlider(state: MutableState<LightmeterState>) {
+fun IsoSlider(state: MutableState<LightmeterState>, recalculateShutterSpeed: () -> Unit) {
     Row(
         modifier = Modifier.padding(all = 8.dp),
         verticalAlignment = Alignment.CenterVertically
@@ -154,6 +163,7 @@ fun IsoSlider(state: MutableState<LightmeterState>) {
             value = state.value.iso.toFloat(),
             onValueChange = { value ->
                 state.value = state.value.copy(iso = value.roundToInt())
+                recalculateShutterSpeed()
             },
             valueRange = 1f..2000f
         )
@@ -169,19 +179,24 @@ val previewlightmeterState = mutableStateOf(
     )
 )
 
+fun previewRecalculateShutterSpeed() {}
+
 @Preview(showBackground = true)
 @Composable
 fun IsoSliderPreview() {
     LightMeterTheme {
         IsoSlider(
-            state = remember { previewlightmeterState }
+            state = remember { previewlightmeterState },
+            recalculateShutterSpeed = { previewRecalculateShutterSpeed() }
         )
     }
 }
 
-// TODO: Recalculate state on change
 @Composable
-fun ApertureSlider(state: MutableState<LightmeterState>) {
+fun ApertureSlider(
+    state: MutableState<LightmeterState>,
+    recalculateShutterSpeed: () -> Unit
+) {
     Row(
         modifier = Modifier.padding(all = 8.dp),
         verticalAlignment = Alignment.CenterVertically
@@ -195,6 +210,7 @@ fun ApertureSlider(state: MutableState<LightmeterState>) {
             value = state.value.aperture.toFloat(),
             onValueChange = { value ->
                 state.value = state.value.copy(aperture = value.toDouble())
+                recalculateShutterSpeed()
             },
             valueRange = 0.85f..22f
         )
@@ -205,12 +221,18 @@ fun ApertureSlider(state: MutableState<LightmeterState>) {
 @Composable
 fun ApertureSliderPreview() {
     LightMeterTheme {
-        ApertureSlider(state = remember { previewlightmeterState })
+        ApertureSlider(
+            state = remember { previewlightmeterState },
+            recalculateShutterSpeed = { previewRecalculateShutterSpeed() }
+        )
     }
 }
 
 @Composable
-fun LightmeterHomeScreen(state: MutableState<LightmeterState>) {
+fun LightmeterHomeScreen(
+    state: MutableState<LightmeterState>,
+    recalculateShutterSpeed: () -> Unit
+) {
     Column(modifier = Modifier
         .fillMaxSize()
         .padding(top = 64.dp)
@@ -245,8 +267,14 @@ fun LightmeterHomeScreen(state: MutableState<LightmeterState>) {
             modifier = Modifier.padding(top = 64.dp),
             verticalArrangement = Arrangement.Bottom
         ) {
-            IsoSlider(state = state)
-            ApertureSlider(state = state)
+            IsoSlider(
+                state = state,
+                recalculateShutterSpeed = recalculateShutterSpeed
+            )
+            ApertureSlider(
+                state = state,
+                recalculateShutterSpeed = recalculateShutterSpeed
+            )
         }
     }
 }
@@ -256,7 +284,8 @@ fun LightmeterHomeScreen(state: MutableState<LightmeterState>) {
 fun LightmeterHomeScreenPreview() {
     LightMeterTheme {
         LightmeterHomeScreen(
-            state = remember { previewlightmeterState }
+            state = remember { previewlightmeterState },
+            recalculateShutterSpeed = { previewRecalculateShutterSpeed() }
         )
     }
 }
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