diff --git a/app/src/main/java/com/example/hpostesting/data/constant/Constants.kt b/app/src/main/java/com/example/hpostesting/data/constant/Constants.kt
index bcef509..33aff22 100644
--- a/app/src/main/java/com/example/hpostesting/data/constant/Constants.kt
+++ b/app/src/main/java/com/example/hpostesting/data/constant/Constants.kt
@@ -74,4 +74,7 @@ object Constants {
     const val BUFFER_VALUE_3 = "BufferValue3"
     const val BUFFER_VALUE_4 = "BufferValue4"
     const val DEVICE_ID = "DEVICE_ID"
+
+    const val BUFFER_LED_LOWER_BOUND = 20000
+    const val BUFFER_LED_HIGHER_BOUND = 24000
 }
\ No newline at end of file
diff --git a/app/src/main/java/com/example/hpostesting/presentation/hemocube/HemoCubeFragment.kt b/app/src/main/java/com/example/hpostesting/presentation/hemocube/HemoCubeFragment.kt
index d56ee51..735fcc6 100644
--- a/app/src/main/java/com/example/hpostesting/presentation/hemocube/HemoCubeFragment.kt
+++ b/app/src/main/java/com/example/hpostesting/presentation/hemocube/HemoCubeFragment.kt
@@ -45,12 +45,13 @@ class HemoCubeFragment : Fragment() {
     private val testingTrace = Firebase.performance.newTrace("testing_trace")
     private var led1BufferForDevice = 0.0
     private var led2BufferForDevice = 0.0
-    private var led3BufferForDevice =  0.0
+    private var led3BufferForDevice = 0.0
     private var led4BufferForDevice = 0.0
     private var led1SampleForDevice = 0.0
     private var led2SampleForDevice = 0.0
-    private var led3SampleForDevice =  0.0
+    private var led3SampleForDevice = 0.0
     private var led4SampleForDevice = 0.0
+    private var validationError = false
 
     override fun onCreateView(
         inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?,
@@ -96,8 +97,8 @@ class HemoCubeFragment : Fragment() {
                 binding.tvSubtitle4.visibility = View.VISIBLE
                 binding.tvSubtitle4.text = "Sample Started"
             }
-                startSampleProcess()
-                it.visibility = View.GONE
+            startSampleProcess()
+            it.visibility = View.GONE
         }
 
         binding.btnPlacebuffer.setOnClickListener {
@@ -355,7 +356,8 @@ class HemoCubeFragment : Fragment() {
                 sampleIntensity = resultLines[7].split(' ')[1].trim()
                 led3SampleForDevice = resultLines[7].split(' ')[1].trim().toDoubleOrNull()!!
                 sampleIntensity = resultLines[8].split(' ')[1].split('\r')[0].trim()
-                led4SampleForDevice = resultLines[8].split(' ')[1].split('\r')[0].trim().toDoubleOrNull()!!
+                led4SampleForDevice =
+                    resultLines[8].split(' ')[1].split('\r')[0].trim().toDoubleOrNull()!!
                 processResult()
             }
         }
@@ -406,9 +408,34 @@ class HemoCubeFragment : Fragment() {
             val led4Average = log10(led4BufferForDevice?.div(led4SampleForDevice!!) ?: 0.0)
             val deviceRatio = led3Average / led1Average
 
-            if (led1Average < 0 || led2Average < 0) {
+            if (led1Average < 0 || led2Average < 0 || led3Average < 0 || led4Average < 0) {
+                validationError = true
                 activity?.runOnUiThread {
-                    binding.errorMessage.text = "Warning: Negative Abs. Retake Blank Reading"
+                    binding.errorMessage.text = "Error: Negative Abs. Retake Blank Reading"
+                    binding.errorMessage.visibility = View.VISIBLE
+                }
+            }
+
+            if (led1BufferForDevice < Constants.BUFFER_LED_LOWER_BOUND
+                || led2BufferForDevice < Constants.BUFFER_LED_LOWER_BOUND
+                || led3BufferForDevice < Constants.BUFFER_LED_LOWER_BOUND
+                || led4BufferForDevice < Constants.BUFFER_LED_LOWER_BOUND
+            ) {
+                validationError = true
+                activity?.runOnUiThread {
+                    binding.errorMessage.text = "Error: Invalid Test. Blank reading is too low"
+                    binding.errorMessage.visibility = View.VISIBLE
+                }
+            }
+
+            if (led1BufferForDevice > Constants.BUFFER_LED_HIGHER_BOUND
+                || led2BufferForDevice > Constants.BUFFER_LED_HIGHER_BOUND
+                || led3BufferForDevice > Constants.BUFFER_LED_HIGHER_BOUND
+                || led4BufferForDevice > Constants.BUFFER_LED_HIGHER_BOUND
+            ) {
+                validationError = true
+                activity?.runOnUiThread {
+                    binding.errorMessage.text = "Error: Invalid Test. Blank reading is too high"
                     binding.errorMessage.visibility = View.VISIBLE
                 }
             }
@@ -444,11 +471,13 @@ class HemoCubeFragment : Fragment() {
                         apply()
                     }
                 }
-                activity?.runOnUiThread {
-                    binding.btnSubmit.visibility = View.VISIBLE
-                    binding.btnSubmit.isEnabled = true
-                    binding.btnSubmit.isClickable = true
-                    binding.clParent.setBackgroundColor(Color.parseColor("#edfffd"))
+                if (!validationError) {
+                    activity?.runOnUiThread {
+                        binding.btnSubmit.visibility = View.VISIBLE
+                        binding.btnSubmit.isEnabled = true
+                        binding.btnSubmit.isClickable = true
+                        binding.clParent.setBackgroundColor(Color.parseColor("#edfffd"))
+                    }
                 }
             }
         } catch (e: Exception) {
@@ -480,14 +509,14 @@ class HemoCubeFragment : Fragment() {
                 if (calculatedRatio > 0.35)
                     return "Inconclusive. Repeat with test with lower volume of blood"
             } else {
-                return "NULL"
+                return "INVALID"
             }
         } catch (e: Exception) {
             showToast("error while performing classification")
             Firebase.crashlytics.recordException(e)
             return "ERROR"
         }
-        return "NULL"
+        return "INVALID"
     }
 
     private fun showToast(message: String) {