diff --git a/src/app/_models/mqtt_base.ts b/src/app/_models/mqtt_base.ts
index 4c79368..9bc4aad 100644
--- a/src/app/_models/mqtt_base.ts
+++ b/src/app/_models/mqtt_base.ts
@@ -56,6 +56,12 @@ export class MQTTEntity implements iMQTTEntityBase {
     }
     return jsonObject;
   }
+
+  get size(): number {
+    this._size = JSON.stringify(this.toJSON()).length;
+    return this._size;
+  }
+
   getProperty(name: string): any {
     if (!this.attrs.has(name)) return;
     return this[name as keyof this];
diff --git a/src/app/_services/output.service.ts b/src/app/_services/output.service.ts
new file mode 100644
index 0000000..761ee31
--- /dev/null
+++ b/src/app/_services/output.service.ts
@@ -0,0 +1,19 @@
+  get device_entity(): MQTTEntity {
+    if (
+      this._device_entity_cached.listlen ===
+      this.generatorService.created_entity_num
+    )
+      return this._device_entity_cached.entity;
+    let entites = Array.from(this.generatorService.created_enteties).sort(
+      (a, b) => {
+        return a.size - b.size;
+      }
+    );
+    this._device_entity_cached = {
+      entity: entites[0],
+      listlen: this.generatorService.created_entity_num,
+    };
+    console.log('sizing');
+    console.log(this._device_entity_cached);
+    return entites[0];
+  }