diff --git a/BluetoothExplorer/Controller/GATT Characteristic Editors/ModelNumberCharacteristicViewController.swift b/BluetoothExplorer/Controller/GATT Characteristic Editors/ModelNumberCharacteristicViewController.swift
index c80ab19..8407725 100644
--- a/BluetoothExplorer/Controller/GATT Characteristic Editors/ModelNumberCharacteristicViewController.swift	
+++ b/BluetoothExplorer/Controller/GATT Characteristic Editors/ModelNumberCharacteristicViewController.swift	
@@ -31,7 +31,7 @@ final class ModelNumberCharacteristicViewController: UIViewController {
     
     // MARK: - Actions
     
-    @IBAction func textFieldEditingChanged(_ sender: Any) {
+    @IBAction func textFieldEditingChanged(_ sender: UITextField) {
         
         guard let text = modelTextField.text
             else { return }
@@ -49,8 +49,9 @@ final class ModelNumberCharacteristicViewController: UIViewController {
         updateText()
     }
     
-    func updateText() {
+    private func updateText() {
         
+        modelTextField.isEnabled = valueDidChange != nil
         modelTextField.text = value.rawValue
     }
 }
diff --git a/BluetoothExplorer/Controller/GATT Characteristic Editors/SystemIDCharacteristicViewController.swift b/BluetoothExplorer/Controller/GATT Characteristic Editors/SystemIDCharacteristicViewController.swift
index 85fc3a9..4a85225 100644
--- a/BluetoothExplorer/Controller/GATT Characteristic Editors/SystemIDCharacteristicViewController.swift	
+++ b/BluetoothExplorer/Controller/GATT Characteristic Editors/SystemIDCharacteristicViewController.swift	
@@ -45,9 +45,12 @@ final class SystemIDCharacteristicViewController: UIViewController {
         guard let organizationallyUniqueIdentifier = UInt32(organizationallyUniqueIdentifierText)
             else { return }
         
-        value = GATTSystemID(manufacturerIdentifier: manufacturerIdentifier,
-                             organizationallyUniqueIdentifier: organizationallyUniqueIdentifier)!
-//        valueDidChange?(value)
+        guard let systemID = GATTSystemID(manufacturerIdentifier: manufacturerIdentifier,
+                                          organizationallyUniqueIdentifier: organizationallyUniqueIdentifier)
+            else { return }
+        
+        value = systemID
+        valueDidChange?(value)
     }
 }