diff --git a/Brightness Sync/AppDelegate.swift b/Brightness Sync/AppDelegate.swift
index cd69fbf..9ad2399 100644
--- a/Brightness Sync/AppDelegate.swift	
+++ b/Brightness Sync/AppDelegate.swift	
@@ -4,79 +4,98 @@ import os
 class AppDelegate: NSObject, NSApplicationDelegate {
     let statusItem = NSStatusBar.system.statusItem(withLength: NSStatusItem.squareLength)
     let statusIndicator = NSMenuItem(title: "Starting", action: nil, keyEquivalent: "")
-    
+
+    let updateInterval = 0.1
     var syncTimer: Timer?
-    
+
     var lastBrightness: Double?
-    
+
+    let brightnessOffsetKey = "BSBrightnessOffset"
+    var brightnessOffset: Double {
+        get {
+            UserDefaults.standard.double(forKey: brightnessOffsetKey)
+        }
+        set (newValue) {
+            UserDefaults.standard.set(newValue, forKey: brightnessOffsetKey)
+        }
+    }
+
     // CoreDisplay_Display_GetUserBrightness reports 1.0 for builtin display just before applicationDidChangeScreenParameters when closing lid.
     // This is a workaround to restore the last sane value after syncing stops.
     var lastSaneBrightness: Double?
     var lastSaneBrightnessDelayTimer: Timer?
-    
+
     static let maxDisplays: UInt32 = 8
-    
+
     func applicationDidFinishLaunching(_ aNotification: Notification) {
         if let button = statusItem.button {
             button.image = #imageLiteral(resourceName: "StatusBarButtonImage")
         }
-        
+
         let menu = NSMenu()
         menu.addItem(statusIndicator)
         menu.addItem(NSMenuItem.separator())
-        
+
+        menu.addItem(NSMenuItem(title: "Brightness Offset", action: nil, keyEquivalent: ""))
+        let menuItem = NSMenuItem()
+        menuItem.view = sliderView
+        menu.addItem(menuItem)
+
+        menu.addItem(NSMenuItem.separator())
+
         let appVersion = Bundle.main.object(forInfoDictionaryKey: "CFBundleShortVersionString") as! String
         menu.addItem(NSMenuItem(title: "v\(appVersion)", action: nil, keyEquivalent: ""))
         menu.addItem(NSMenuItem(title: "Check For Updates", action: #selector(checkForUpdates), keyEquivalent: ""))
         menu.addItem(NSMenuItem.separator())
-        
+
         let copyDiagnosticsButton = NSMenuItem(title: "Copy Diagnostics", action: #selector(copyDiagnosticsToPasteboard), keyEquivalent: "c")
         copyDiagnosticsButton.isHidden = true
         copyDiagnosticsButton.allowsKeyEquivalentWhenHidden = true
         menu.addItem(copyDiagnosticsButton)
-        
+
         menu.addItem(NSMenuItem(title: "Quit", action: #selector(NSApplication.terminate), keyEquivalent: ""))
         statusItem.menu = menu
-        
+
         refresh()
     }
-    
+
     func applicationWillTerminate(_ aNotification: Notification) {
         // Insert code here to tear down your application
     }
-    
+
     func applicationDidChangeScreenParameters(_ notification: Notification) {
         refresh()
     }
-    
+
     func refresh() {
         os_log("Starting display refresh...")
-        
+
         let allDisplays = AppDelegate.getAllDisplays()
         let lgDisplayIdentifiers = AppDelegate.getConnectedUltraFineDisplayIdentifiers()
-        
+
         let builtin = allDisplays.first { CGDisplayIsBuiltin($0) == 1 }
         let syncTo = allDisplays.filter { lgDisplayIdentifiers.contains(DisplayIdentifier(vendorNumber: CGDisplayVendorNumber($0), modelNumber: CGDisplayModelNumber($0))) }
-        
+
         syncTimer?.invalidate()
-        
+
         if let syncFrom = builtin, !syncTo.isEmpty {
-            syncTimer = Timer.scheduledTimer(withTimeInterval: 0.1, repeats: true) { (_) -> Void in
-                let newBrightness = CoreDisplay_Display_GetUserBrightness(syncFrom)
-                
+            syncTimer = Timer(timeInterval: updateInterval, repeats: true) { (_) in
+                let sourceBrightness = CoreDisplay_Display_GetUserBrightness(syncFrom)
+                let newBrightness = (sourceBrightness + self.brightnessOffset).clamped(to: 0.0...1.0)
+
                 if let oldBrightness = self.lastBrightness, abs(oldBrightness - newBrightness) < 0.01 {
                     return
                 }
-                
+
                 for display in syncTo {
                     CoreDisplay_Display_SetUserBrightness(display, newBrightness)
                 }
-                
+
                 self.lastBrightness = newBrightness
-                
+
                 if newBrightness == 1, self.lastSaneBrightness != 1 {
                     let timerAlreadyRunning = self.lastSaneBrightnessDelayTimer?.isValid ?? false
-                    
+
                     if !timerAlreadyRunning {
                         self.lastSaneBrightnessDelayTimer = Timer.scheduledTimer(withTimeInterval: 2, repeats: false) { (_) -> Void in
                             self.lastSaneBrightness = newBrightness
@@ -88,7 +107,8 @@ class AppDelegate: NSObject, NSApplicationDelegate {
                     self.lastSaneBrightness = newBrightness
                 }
             }
-            
+            RunLoop.current.add(syncTimer!, forMode: .common)
+
             statusIndicator.title = "Activated"
             os_log("Activated...")
         }
@@ -100,24 +120,24 @@ class AppDelegate: NSObject, NSApplicationDelegate {
                 }
                 lastSaneBrightness = nil
             }
-            
+
             statusIndicator.title = "Deactivated"
             os_log("Deactivated...")
         }
     }
-    
+
     static func getAllDisplays() -> [CGDirectDisplayID] {
         var onlineDisplays = [CGDirectDisplayID](repeating: 0, count: Int(maxDisplays))
         var displayCount: UInt32 = 0
-        
+
         CGGetOnlineDisplayList(maxDisplays, &onlineDisplays, &displayCount)
-        
+
         return Array(onlineDisplays[0..<Int(displayCount)])
     }
-    
+
     static func getConnectedUltraFineDisplayIdentifiers() -> Set<DisplayIdentifier> {
         var ultraFineDisplays = Set<DisplayIdentifier>()
-        
+
         for displayInfo in getDisplayInfoDictionaries() {
             if
                 let displayNames = displayInfo[kDisplayProductName] as? NSDictionary,
@@ -139,39 +159,39 @@ class AppDelegate: NSObject, NSApplicationDelegate {
                 os_log("Display without en_US name found.")
             }
         }
-        
+
         return ultraFineDisplays
     }
-    
+
     static func getDisplayInfoDictionaries() -> [NSDictionary] {
         var diplayInfoDictionaries = [NSDictionary]()
-        
+
         var iterator: io_iterator_t = 0
         guard IOServiceGetMatchingServices(kIOMasterPortDefault, IOServiceMatching("IODisplayConnect"), &iterator) == 0 else {
             return diplayInfoDictionaries
         }
-        
+
         var display = IOIteratorNext(iterator)
-        
+
         while display != 0 {
             if let displayInfo = IODisplayCreateInfoDictionary(display, 0)?.takeRetainedValue() as NSDictionary? {
                 diplayInfoDictionaries.append(displayInfo)
             }
-            
+
             IOObjectRelease(display)
-            
+
             display = IOIteratorNext(iterator)
         }
-        
+
         IOObjectRelease(iterator)
-        
+
         return diplayInfoDictionaries
     }
-    
+
     @objc func copyDiagnosticsToPasteboard() {
         let CGDisplays = AppDelegate.getAllDisplays()
         let IODisplays = AppDelegate.getDisplayInfoDictionaries()
-        
+
         let diagnostics = """
         CGDisplayList:
         \(CGDisplays.map {
@@ -179,21 +199,55 @@ class AppDelegate: NSObject, NSApplicationDelegate {
         "ModelNumber": CGDisplayModelNumber($0),
         "SerialNumber": CGDisplaySerialNumber($0)]
         })
-        
+
         IODisplayList:
         \(IODisplays)
         """
-        
+
         NSPasteboard.general.clearContents()
         NSPasteboard.general.setString(diagnostics, forType: .string)
     }
-    
+
     @objc func checkForUpdates() {
         NSWorkspace.shared.open(URL(string: "https://github.com/OCJvanDijk/Brightness-Sync/releases")!)
     }
-    
+
+    @objc func brightnessOffsetUpdated(slider: NSSlider) {
+        brightnessOffset = slider.doubleValue
+        syncTimer?.fire()
+    }
+
     struct DisplayIdentifier: Hashable {
         let vendorNumber: UInt32
         let modelNumber: UInt32
     }
+
+    private lazy var sliderView: NSView = {
+        let container = NSView(frame: NSRect(origin: CGPoint.zero, size: CGSize(width: 160, height: 28)))
+
+        let updateSel = #selector(brightnessOffsetUpdated(slider:))
+        let statusSlider = NSSlider(value: brightnessOffset, minValue: -0.5, maxValue: 0.5, target: self, action: updateSel)
+        container.addSubview(statusSlider)
+        statusSlider.translatesAutoresizingMaskIntoConstraints = false
+
+        statusSlider.leadingAnchor.constraint(equalTo: container.leadingAnchor, constant: 20).isActive = true
+        statusSlider.trailingAnchor.constraint(equalTo: container.trailingAnchor).isActive = true
+        statusSlider.topAnchor.constraint(equalTo: container.topAnchor).isActive = true
+        statusSlider.bottomAnchor.constraint(equalTo: container.bottomAnchor).isActive = true
+
+
+        return container
+    }()
+}
+
+extension Comparable {
+    func clamped(to limits: ClosedRange<Self>) -> Self {
+        return min(max(self, limits.lowerBound), limits.upperBound)
+    }
+}
+
+extension Strideable where Stride: SignedInteger {
+    func clamped(to limits: CountableClosedRange<Self>) -> Self {
+        return min(max(self, limits.lowerBound), limits.upperBound)
+    }
 }