diff --git a/js/faradays-law/model/Voltmeter.js b/js/faradays-law/model/Voltmeter.js
index 651623d1..ad371773 100644
--- a/js/faradays-law/model/Voltmeter.js
+++ b/js/faradays-law/model/Voltmeter.js
@@ -16,26 +16,29 @@ define( function( require ) {
 
   // constants
   var ACTIVITY_THRESHOLD = 1E-3; // Used to prevent perpetual oscillation of the needle, value empirically determined.
+  var NEEDLE_RESPONSIVENESS = 50;  // needle responsiveness
+  var NEEDLE_FRICTION = 10; // friction coefficient, so needle motion looks realistic
 
   /**
-   * @param faradaysLawModel - simulation model
+   * @param {FaradaysLawModel} model - simulation model
    * @param {Tandem} tandem
    * @constructor
    */
-  function Voltmeter( faradaysLawModel, tandem ) {
+  function Voltmeter( model, tandem ) {
 
-    this.faradaysLawModel = faradaysLawModel;
+    // @private
+    this.model = model;
 
-    this.omega = 0; // angular velocity of needle in rad/sec
-    this.alpha = 0; // angular acceleration of needle in rad/s^2
-    this.D = 50;  // needle responsiveness
-    this.C = 1;   // meter gain
-    this.B = 10; // friction coefficient, so needle motion looks realistic
+    // @private {number} - rad/sec
+    this.needleAngularVelocity = 0;
 
-    // Needle angle in radians. This apparently drives both the needle location and the lightbulb brightness.
+    // @private {number} - rad/s^2
+    this.needleAngularAcceleration = 0;
+
+    // @public {NumberProperty} Needle angle in radians. This drives both the needle location and the light bulb brightness.
     this.thetaProperty = new NumberProperty( 0 );
 
-    // input voltage to meter
+    // @private - input voltage to meter
     this.signalProperty = new NumberProperty( 0, {
       tandem: tandem.createTandem( 'signalProperty' ),
       units: 'volts'
@@ -45,30 +48,31 @@ define( function( require ) {
   faradaysLaw.register( 'Voltmeter', Voltmeter );
 
   return inherit( Object, Voltmeter, {
+
     /**
-     * voltmeter needle evolution over time
+     * Voltmeter needle evolution over time
      * @param dt
      */
     step: function( dt ) {
 
       // Calculate the signal, combining the EMF from both coils.  The multiplier (including the sign thereof) is
       // empirically determined to make the needle move the correct amount and direction.
-      this.signalProperty.set( -0.2 * (this.faradaysLawModel.bottomCoil.emfProperty.get() + this.faradaysLawModel.topCoil.emfProperty.get()) );
+      this.signalProperty.set( -0.2 * (this.model.bottomCoil.emfProperty.get() + this.model.topCoil.emfProperty.get()) );
 
-      this.alpha = this.D * (this.signalProperty.get() - this.C * this.thetaProperty.get()) - this.B * this.omega; //angular acceleration of needle
-      this.thetaProperty.set( this.thetaProperty.get() + this.omega * dt + 0.5 * this.alpha * dt * dt ); //angle of needle
-      var omegaTemp = this.omega + this.alpha * dt;
-      var alphaTemp = this.D * (this.signalProperty.get() - this.C * this.thetaProperty.get()) - this.B * omegaTemp;
-      this.omega = this.omega + 0.5 * dt * (this.alpha + alphaTemp); //angular velocity
+      this.needleAngularAcceleration = NEEDLE_RESPONSIVENESS * (this.signalProperty.get() - this.thetaProperty.get()) - NEEDLE_FRICTION * this.needleAngularVelocity; //angular acceleration of needle
+      this.thetaProperty.set( this.thetaProperty.get() + this.needleAngularVelocity * dt + 0.5 * this.needleAngularAcceleration * dt * dt ); //angle of needle
+      var omega = this.needleAngularVelocity + this.needleAngularAcceleration * dt;
+      var alpha = NEEDLE_RESPONSIVENESS * (this.signalProperty.get() - this.thetaProperty.get()) - NEEDLE_FRICTION * omega;
+      this.needleAngularVelocity = this.needleAngularVelocity + 0.5 * dt * (this.needleAngularAcceleration + alpha);
 
       // Clamp the needle angle when its position, velocity, and acceleration go below a threshold so that it doesn't
       // oscillate forever.
-      if ( Math.abs( this.alpha ) !== 0 && Math.abs( this.alpha ) < ACTIVITY_THRESHOLD &&
-           Math.abs( this.omega ) !== 0 && Math.abs( this.omega ) < ACTIVITY_THRESHOLD &&
+      if ( Math.abs( this.needleAngularAcceleration ) !== 0 && Math.abs( this.needleAngularAcceleration ) < ACTIVITY_THRESHOLD &&
+           Math.abs( this.needleAngularVelocity ) !== 0 && Math.abs( this.needleAngularVelocity ) < ACTIVITY_THRESHOLD &&
            Math.abs( this.thetaProperty.get() ) !== 0 && Math.abs( this.thetaProperty.get() ) < ACTIVITY_THRESHOLD ) {
         this.thetaProperty.set( 0 );
-        this.omega = 0;
-        this.alpha = 0;
+        this.needleAngularVelocity = 0;
+        this.needleAngularAcceleration = 0;
       }
     }
   } );