Added tare() command to zero the scale

README.md

@@ -3,47 +3,58 @@ WebScale
 
 Measure weight using a Stamps.com digital USB postage scale.
 
-![Stamps.com 5-pound digital postage scale](http://store.stamps.com/web/images/catalog/sku/SC05500000_small.jpg)
+![Stamps.com 5-pound digital postage scale](.github/images/SC05500000_small.jpg)
+
+## Hardware
+*I successfully performed these steps in [September 2014](https://twitter.com/Aldaviva/status/516771809962651648). Today, it may work differently, or not at all.*
 
-# Hardware
 1. Sign up for free trial at [Stamps.com](https://registration.stamps.com/registration/).
-2. During signup, request a complimentary [5-pound digital postage scale](http://store.stamps.com/Store/catalog/product4.jsp?id=5lb-digital-postal-scale). Pay $9.99 shipping and handling.
-3. Before the four-week trial is up, [cancel your account](https://stamps.custhelp.com/app/answers/detail/a_id/114/kw/cancel) and avoid the monthly fee.
+2. During signup, request a complimentary [5-pound digital postage scale](https://store.stamps.com/collections/hardware/products/5lb-scale). Pay $9.99 USD shipping and handling.
+3. Before the four-week trial is up, [cancel your account](https://www.stamps.com/postage-online/faqs/) and avoid the monthly fee.
 
-# Installation
-    $ npm install webscale
+## Installation
+[This package is available on npm.](https://www.npmjs.com/package/webscale)
+```sh
+$ npm install webscale
+```
 In the event of installation trouble, refer to the [node-hid documentation](https://github.com/node-hid/node-hid/blob/master/README.md).
 
-# Usage
+## Usage
 ```javascript
-var WebScale = require('webscale');
-var webScale = new WebScale();
+const WebScale = require('webscale');
+const webScale = new WebScale();
 
-webScale.on('change:weight', function(ounces){
-    console.log(ounces + ' oz.');
+webScale.on('change:weight', ounces => {
+    console.log(`${ounces} oz.`);
 });
 ```
-See also `test-client.js`.
+See also [`test-client.js`](https://github.com/Aldaviva/webscale/blob/master/test-client.js).
 
-# Events
+## Events
 
-## change:weight
+### change:weight
 Called whenever the scale's weight reading changes.
-### Arguments
-- **ounces** how much weight is on the scale, in ounces. Can be negative if the scale was tared with weight on it.
+#### Arguments
+- **ounces** how much weight is on the scale, in ounces. Floating-point number with precision of one digit after the decimal place (tenths of ounces). Can be negative if the scale was tared with weight on it.
 
-## connected
+### connected
 Called when the program first starts and connects successfully to the device, or when it reconnects after losing the connection.
 
-## disconnected
+### disconnected
 Called when the device is unplugged or powered off, and once per reconnect attempt.
 
-## error
+### error
 An error with the USB device occurred (except disconnections, see above).
-### Arguments
+#### Arguments
 - **error** The error from node-hid.
 
-# Methods
+## Methods
 
-## disconnect()
+### tare()
+Reset the scale so the current weight will be read as zero. The scale will also automatically tare itself each time it powers on.
+
+### disconnect()
 Disconnect from the USB device.
+
+## See Also
+- **[Aldaviva/WebScale.net](https://github.com/Aldaviva/WebScale.net)** - this library ported from Node.js to .NET

index.js

@@ -5,47 +5,46 @@ var events = require('events');
 var VENDOR_ID = 9332;
 var PRODUCT_ID = 1360;
 
-
 function WebScale(deviceIndex){
     this._prevWeight = null;
     this._deviceIndex = deviceIndex || 0;
     this._device = null;
 
-    this._connectWithRetry();
+    setTimeout(this._connectWithRetry.bind(this), 0);
 }
 
 util.inherits(WebScale, events.EventEmitter);
 
 WebScale.prototype.disconnect = function(){
     if(this._device){
-	this.emit('disconnected');
-	this._device.close();
-	this._device = null;
+        this.emit('disconnected');
+        this._device.close();
+        this._device = null;
     }
 };
 
 WebScale.prototype._connectWithRetry = function(){
     try {
-	this._connect();
+        this._connect();
     } catch(e){
-	setTimeout(this._connectWithRetry.bind(this), 2000);
+        setTimeout(this._connectWithRetry.bind(this), 2000);
     }
 };
 
 WebScale.prototype._connect = function(){
     var devices = HID.devices(VENDOR_ID, PRODUCT_ID);
 
     if(!devices.length || !devices[this._deviceIndex]){
-	this.emit('disconnected');
-	throw new Error('could not find device');
+        this.emit('disconnected');
+        throw new Error('could not find device');
     }
 
     var devicePath = devices[this._deviceIndex].path;
     try {
-	this._device = new HID.HID(devicePath);
+        this._device = new HID.HID(devicePath);
     } catch(e){
-	this.emit('disconnected');
-	throw e;
+        this.emit('disconnected');
+        throw e;
     }
     this._onConnect(this._device);
 };
@@ -60,18 +59,22 @@ WebScale.prototype._onData = function(data){
     var ounces = data.readInt16LE(4)/10;
 
     if(this._prevWeight !== ounces){
-	this._prevWeight = ounces;
-	this.emit('change:weight', ounces);
+        this._prevWeight = ounces;
+        this.emit('change:weight', ounces);
     }
 };
 
 WebScale.prototype._onError = function(error){
     if(error.message == 'could not read from HID device'){
-	this.emit('disconnected', error);
-	this._connectWithRetry();
+        this.emit('disconnected', error);
+        this._connectWithRetry();
     } else {
-	this.emit('error', error);
+        this.emit('error', error);
     }
 };
 
+WebScale.prototype.tare = function(){
+    this._device.write([0x04, 0x01]);
+};
+
 module.exports = WebScale;