diff --git a/package.json b/package.json
index 9587e89..00ae102 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,7 @@
   "name": "chameleon-ultra.js",
   "repository": "git@github.com:taichunmin/chameleon-ultra.js.git",
   "unpkg": "dist/iife/index.min.js",
-  "version": "0.1.17",
+  "version": "0.1.18",
   "bugs": {
     "url": "https://github.com/taichunmin/chameleon-ultra.js/issues"
   },
diff --git a/src/ChameleonUltra.ts b/src/ChameleonUltra.ts
index ec2b23e..c5e6d81 100644
--- a/src/ChameleonUltra.ts
+++ b/src/ChameleonUltra.ts
@@ -7,7 +7,7 @@ import * as Decoder from './ResponseDecoder'
 
 const READ_DEFAULT_TIMEOUT = 5e3
 const START_OF_FRAME = new Buffer(2).writeUInt16BE(0x11EF)
-const VERSION_SUPPORTED = { gte: '1.0', lt: '2.0' }
+const VERSION_SUPPORTED = { gte: '1.0', lt: '2.0' } as const
 
 /**
  * The core library of "chameleon-ultra.js". The instance of this class must use exactly one adapter plugin to communication to ChameleonUltra.
@@ -62,14 +62,9 @@ export class ChameleonUltra {
   supportedCmds: Set<Cmd> = new Set<Cmd>()
 
   /**
-   * The firmware version of device.
+   * The supported version of SDK.
    */
-  appVersion?: string
-
-  /**
-   * The git version of firmware.
-   */
-  gitVersion?: string
+  static VERSION_SUPPORTED = VERSION_SUPPORTED
 
   /**
    * Create a new instance of ChameleonUltra.
@@ -227,8 +222,6 @@ export class ChameleonUltra {
         try {
           // clean up
           this.supportedCmds.clear()
-          this.appVersion = undefined
-          this.gitVersion = undefined
 
           // close port
           this.rxSink?.controller.abort(err)