From c2e1ec8b827e688491ab319f41fc6c7423e67006 Mon Sep 17 00:00:00 2001
From: samreid <reids@colorado.edu>
Date: Mon, 14 Jan 2019 22:01:03 -0700
Subject: [PATCH] Rewrite calibration in terms of CALIBRATION_SCALE, see
 https://github.com/phetsims/wave-interference/issues/315

---
 js/common/WaveInterferenceConstants.js | 15 +++++++--------
 js/common/model/SoundScene.js          |  4 ++--
 js/waves/model/WavesModel.js           |  2 +-
 3 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/js/common/WaveInterferenceConstants.js b/js/common/WaveInterferenceConstants.js
index 2d031424..5f320ddb 100644
--- a/js/common/WaveInterferenceConstants.js
+++ b/js/common/WaveInterferenceConstants.js
@@ -24,6 +24,10 @@ define( require => {
   const MAJOR_TICK_LENGTH = 12;
   const LATTICE_PADDING = 20;
 
+  // the simulation was initially calibrated at a lattice size of 101-20x2.  This scale factor maintains the same
+  // calibrated behavior for differing lattice sizes.
+  const CALIBRATION_SCALE = ( WaveInterferenceQueryParameters.latticeSize - LATTICE_PADDING * 2 ) / ( 101 - 20 * 2 );
+
   const WaveInterferenceConstants = {
     WAVE_AREA_WIDTH: 500,
     MAJOR_TICK_LENGTH: MAJOR_TICK_LENGTH,
@@ -72,10 +76,7 @@ define( require => {
     FEMTO: 1E-15,
 
     // Cell that oscillates, specified as an offset from the origin of the lattice (includes damping region).
-    POINT_SOURCE_HORIZONTAL_COORDINATE:
-      Util.roundSymmetric(
-      3 / 61 * ( WaveInterferenceQueryParameters.latticeSize - LATTICE_PADDING * 2 ) + LATTICE_PADDING
-      ) + 1,
+    POINT_SOURCE_HORIZONTAL_COORDINATE: Util.roundSymmetric( 3 * CALIBRATION_SCALE ) + LATTICE_PADDING,
 
     // The lattice must have an odd dimension, so that there can be a cell exactly in the middle (for a single-cell
     // oscillator), symmetry for the two oscillator screen, and so the 1-cell wide barrier can appear directly in the
@@ -95,10 +96,8 @@ define( require => {
     // rest of the texts
     TIME_AND_LENGTH_SCALE_INDICATOR_FONT: new PhetFont( DEFAULT_FONT_SIZE - 1 ),
 
-    // tuned so that the time for the wave to pass across the lattice is the same as pre-1.0.  If the lattice size is
-    // changed, this can be re-tuned by computing the time it takes a sound wave to cross the new lattice size and
-    // dividing by the prior time.
-    SCALE_FACTOR: 54.176 / 20
+    // see above
+    CALIBRATION_SCALE: CALIBRATION_SCALE
   };
 
   assert && assert( WaveInterferenceConstants.LATTICE_DIMENSION % 2 === 1, 'lattice dimension must be odd' );
diff --git a/js/common/model/SoundScene.js b/js/common/model/SoundScene.js
index 3329cd49..344668d2 100644
--- a/js/common/model/SoundScene.js
+++ b/js/common/model/SoundScene.js
@@ -111,8 +111,8 @@ define( require => {
           const fy = gradientY * k;
           if ( !isNaN( fx ) && !isNaN( fy ) ) {
             soundParticle.applyForce(
-              fx * WaveInterferenceConstants.SCALE_FACTOR,
-              fy * WaveInterferenceConstants.SCALE_FACTOR,
+              fx * WaveInterferenceConstants.CALIBRATION_SCALE,
+              fy * WaveInterferenceConstants.CALIBRATION_SCALE,
               dt, this
             );
           }
diff --git a/js/waves/model/WavesModel.js b/js/waves/model/WavesModel.js
index 8c7cae0b..def00425 100644
--- a/js/waves/model/WavesModel.js
+++ b/js/waves/model/WavesModel.js
@@ -54,7 +54,7 @@ define( require => {
   // This simulation uses EventTimer, which provides exactly the same model behavior on very slow and very fast
   // platforms.  Here we define the frequency of events in Hz, which has been tuned so that iPad2 has enough time to run
   // model computations.
-  const EVENT_RATE = 20 * WaveInterferenceConstants.SCALE_FACTOR;
+  const EVENT_RATE = 20 * WaveInterferenceConstants.CALIBRATION_SCALE;
   const toFemto = WaveInterferenceUtils.toFemto;
 
   class WavesModel {