diff --git a/js/demo/sim-like-components/model/BoxOfBalls.ts b/js/demo/sim-like-components/model/BoxOfBalls.ts
index fdcc8818..b4609c2f 100644
--- a/js/demo/sim-like-components/model/BoxOfBalls.ts
+++ b/js/demo/sim-like-components/model/BoxOfBalls.ts
@@ -26,15 +26,15 @@ const createRandomColor = () => {
 };
 
 class BoxOfBalls {
+
+  // an array the contains the balls that are in this box
+  public readonly balls: ObservableArray<Ball>;
+
+  // the bounding box
   private readonly box: Shape;
-  private readonly balls: ObservableArray<Ball>;
 
   constructor( width: number, height: number ) {
-
-    // @public (read-only) {Shape.rect} - the bounding box
     this.box = Shape.rect( 50, 0, width, height );
-
-    // @public (read-only) {ObservableArrayDef}
     this.balls = createObservableArray();
   }
 
diff --git a/js/demo/sim-like-components/model/SimLikeComponentsModel.ts b/js/demo/sim-like-components/model/SimLikeComponentsModel.ts
index 2583b2ba..ed5b5c50 100644
--- a/js/demo/sim-like-components/model/SimLikeComponentsModel.ts
+++ b/js/demo/sim-like-components/model/SimLikeComponentsModel.ts
@@ -1,7 +1,5 @@
 // Copyright 2018-2020, University of Colorado Boulder
 
-// @ts-nocheck
-
 /**
  * A model that exists only for the purposes of demonstrating sonification, particularly how view and model elements are
  * used together to hook up sonification elements.
@@ -16,24 +14,26 @@ import BoxOfBalls from './BoxOfBalls.js';
 
 class SimLikeComponentsModel {
 
-  /**
-   * @constructor
-   */
-  constructor() {
+  // a box containing bouncing balls
+  public readonly boxOfBalls: BoxOfBalls;
 
-    // @public (read-only) {BoxOfBalls) - box containing bouncing balls, size empirically determined
-    this.boxOfBalls = new BoxOfBalls( 135, 80 );
+  // controls the number of balls in the box
+  public readonly numberOfBallsProperty: NumberProperty;
 
-    // @public {NumberProperty} - controls the number of balls in the box
-    this.numberOfBallsProperty = new NumberProperty( 0 );
+  // controls whether the balls are bouncing around in the box or still
+  public readonly ballsMovingProperty: BooleanProperty;
 
-    // @public {BooleanProperty} - controls whether the balls are bouncing around in the box or still
-    this.ballsMovingProperty = new BooleanProperty( false );
+  // tracks whether a reset is happening
+  public readonly resetInProgressProperty: BooleanProperty;
 
-    // @public {BooleanProperty} - tracks whether a reset is happening
+  constructor() {
+
+    this.boxOfBalls = new BoxOfBalls( 135, 80 ); // size empirically determined
+    this.numberOfBallsProperty = new NumberProperty( 0 );
+    this.ballsMovingProperty = new BooleanProperty( false );
     this.resetInProgressProperty = new BooleanProperty( false );
 
-    // add or remove balls as the count changes
+    // Add or remove balls as the count changes.
     this.numberOfBallsProperty.link( desiredNumberOfBalls => {
       const numberBallsInBox = this.boxOfBalls.balls.lengthProperty.get();
       if ( desiredNumberOfBalls > numberBallsInBox ) {
@@ -50,10 +50,10 @@ class SimLikeComponentsModel {
   }
 
   /**
-   * @param {number} dt - delta time, in seconds
+   * @param dt - delta time, in seconds
    * @public
    */
-  step( dt ) {
+  step( dt: number ) {
     if ( this.ballsMovingProperty.value ) {
       this.boxOfBalls.step( dt );
     }
@@ -68,7 +68,6 @@ class SimLikeComponentsModel {
     this.ballsMovingProperty.reset();
     this.resetInProgressProperty.value = false;
   }
-
 }
 
 tambo.register( 'SimLikeComponentsModel', SimLikeComponentsModel );