diff --git a/Sources/Models/State.swift b/Sources/Models/State.swift
new file mode 100644
index 0000000..574b38b
--- /dev/null
+++ b/Sources/Models/State.swift
@@ -0,0 +1,67 @@
+import Foundation
+import CoreUnitTypes
+
+public struct State: Equatable {
+  
+  @TrackedChanges
+  public var temperature: Temperature?
+  
+  @TrackedChanges
+  public var humidity: RelativeHumidity?
+  
+  public init(
+    temperature: Temperature? = nil,
+    humidity: RelativeHumidity? = nil,
+    needsProcessed: Bool = false
+  ) {
+    self._temperature = .init(wrappedValue: temperature, needsProcessed: needsProcessed)
+    self._humidity = .init(wrappedValue: humidity, needsProcessed: needsProcessed)
+  }
+  
+  public var needsProcessed: Bool {
+    $temperature.needsProcessed || $humidity.needsProcessed
+  }
+}
+
+@propertyWrapper
+public struct TrackedChanges<Value> {
+  
+  private var tracking: TrackingState
+  private var value: Value
+  
+  public var wrappedValue: Value {
+    get { value }
+    set {
+      // fix
+      value = newValue
+    }
+  }
+  
+  public init(wrappedValue: Value, needsProcessed: Bool = false) {
+    self.value = wrappedValue
+    self.tracking = needsProcessed ? .needsProcessed : .hasProcessed
+  }
+  
+  enum TrackingState {
+    case hasProcessed
+    case needsProcessed
+  }
+  
+  public var needsProcessed: Bool {
+    get { tracking == .needsProcessed }
+    set {
+      if newValue {
+        tracking = .needsProcessed
+      } else {
+        tracking = .hasProcessed
+      }
+    }
+  }
+  
+  public var projectedValue: Self {
+    get { self }
+    set { self = newValue }
+  }
+}
+
+extension TrackedChanges: Equatable where Value: Equatable { }