diff --git a/src/javascript/sim5.js b/src/javascript/sim5.js
index 3bfdc95..8dd3571 100644
--- a/src/javascript/sim5.js
+++ b/src/javascript/sim5.js
@@ -7,6 +7,7 @@ const c = cvs.getContext('2d');
 const wavelengthInput = document.getElementById("wavelengthInput_DS");
 const slitWidthInput = document.getElementById("slitWidthInput_DS");
 const slitSeparationInput = document.getElementById("slitSeparationInput_DS");
+const envelopeInput = document.getElementById("envelopeInput_DS");
 
 const simulation = new DoubleSlitSimulation(cvs, c)
 const animate = () => {
@@ -32,5 +33,9 @@ slitSeparationInput.oninput = () => {
     simulation.setSlitSeparation(slitSeparationInput.value / 1_000_000);
 }
 
+envelopeInput.oninput = () => {
+    simulation.setEnvelope(envelopeInput.checked);
+}
+
 
 animate()
\ No newline at end of file
diff --git a/src/javascript/sim6.js b/src/javascript/sim6.js
index 318e4c5..b9127f0 100644
--- a/src/javascript/sim6.js
+++ b/src/javascript/sim6.js
@@ -8,6 +8,7 @@ const slitsInput = document.getElementById("slitsInput_nSlit");
 const wavelengthInput = document.getElementById("wavelengthInput_nSlit");
 const slitWidthInput = document.getElementById("slitWidthInput_nSlit");
 const slitSeparationInput = document.getElementById("slitSeparationInput_nSlit");
+const envelopeInput = document.getElementById("envelopeInput_nSlit");
 
 const simulation = new NSlitSimulation(cvs, c)
 const animate = () => {
@@ -38,5 +39,9 @@ slitsInput.oninput = () => {
     simulation.setSlits(slitsInput.value);
 }
 
+envelopeInput.oninput = () => {
+    simulation.setEnvelope(envelopeInput.checked);
+}
+
 
 animate()
\ No newline at end of file
diff --git a/src/javascript/simulations/doubleSlit.js b/src/javascript/simulations/doubleSlit.js
index 901c158..62cae4e 100644
--- a/src/javascript/simulations/doubleSlit.js
+++ b/src/javascript/simulations/doubleSlit.js
@@ -10,6 +10,7 @@ class DoubleSlitSimulation extends Simulation {
         this.wavelength = wavelength;
         this.slitWidth = slitWidth;
         this.slitSeparation = slitSeparation;
+        this.envelope = 1;
         this.color = w2h(this.wavelength);
 
         this.t = 0;
@@ -25,19 +26,30 @@ class DoubleSlitSimulation extends Simulation {
             this.slitWidth / this.ypx2m, this.slitSeparation / this.ypx2m);
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
     }
 
     evaluate = (theta) => {
         theta = Math.round(theta * 1_000_000) / 1_000_000;
         if (theta in this.cache) return this.cache[theta];
         const sine = Math.sin(theta);
-        const cs = Math.cos(Math.PI * this.slit.separation * this.ypx2m * sine / this.wavelength);
+        const cs = Math.cos(Math.PI * (this.slit.separation + this.slit.width) * this.ypx2m * sine / this.wavelength);
         const a = Math.PI * this.slit.width * this.ypx2m * sine / this.wavelength
         const tmp = Math.sin(a) / a;
         this.cache[theta] = cs * cs * tmp * tmp;
         return this.cache[theta];
     }
 
+    evaluateEnvelope = (theta) => {
+        theta = Math.round(theta * 1_000_00) / 1_000_00;
+        if (theta in this.cacheEnvelope) return this.cacheEnvelope[theta];
+        let sine = Math.sin(theta);
+        let a = Math.PI * this.slit.width * this.ypx2m * sine / this.wavelength;
+        let tmp = Math.sin(a) / a;
+        this.cacheEnvelope[theta] = tmp * tmp;
+        return this.cacheEnvelope[theta];
+    }
+
     update = () => {
         this.t += this.dt;
 
@@ -46,6 +58,7 @@ class DoubleSlitSimulation extends Simulation {
             this.screen.draw();
             this.slit.draw();
             this.plotIntensity();
+            if (this.envelope) this.plotEnvelope();
             this.redraw = false;
         } else this.c.clearRect(this.slit.x + 2.5, 0, this.screen.x - this.slit.x - 5, this.cvs.height);
 
@@ -75,11 +88,25 @@ class DoubleSlitSimulation extends Simulation {
         this.c.stroke();
     }
 
+    plotEnvelope = () => {
+        this.c.beginPath();
+        this.c.lineWidth = 1;
+        this.c.strokeStyle = "#FFFFFF";
+        for (let y = 0; y <= this.cvs.height; y++) {
+            const theta = Math.atan2((y - this.slit.y) * this.ypx2m, (this.screen.x - this.slit.x) * this.xpx2m);
+            const intensity =  this.evaluateEnvelope(theta) * this.cvs.width / 10;
+            if (y === 0) this.c.moveTo(this.screen.x + 5 + intensity, y);
+            else this.c.lineTo(this.screen.x + 5 + intensity, y);
+        }
+        this.c.stroke();
+    }
+
     displayMeasurements = () => {
         this.c.save();
         this.c.beginPath();
         this.c.moveTo(this.slit.x, this.cvs.height * 0.9);
         this.c.lineTo(this.screen.x, this.cvs.height * 0.9);
+        this.c.lineWidth = 3;
         this.c.strokeStyle = "#179e7e";
         this.c.stroke();
         this.c.translate((this.slit.x + this.screen.x) / 2, this.cvs.height * 0.9 - 18);
@@ -96,6 +123,7 @@ class DoubleSlitSimulation extends Simulation {
         this.color = w2h(wavelength);
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
     }
 
     setSlitWidth = (slitWidth) => {
@@ -103,6 +131,7 @@ class DoubleSlitSimulation extends Simulation {
         this.slit.width = slitWidth / this.ypx2m;
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
     }
 
     setSlitSeparation = (slitSeparation) => {
@@ -110,6 +139,12 @@ class DoubleSlitSimulation extends Simulation {
         this.slit.separation = slitSeparation / this.ypx2m;
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
+    }
+
+    setEnvelope = (envelope) => {
+        this.envelope = envelope;
+        this.redraw = true;
     }
 
     intensityAt = (x, y) => {
diff --git a/src/javascript/simulations/nSlit.js b/src/javascript/simulations/nSlit.js
index 400c5da..7a31ccc 100644
--- a/src/javascript/simulations/nSlit.js
+++ b/src/javascript/simulations/nSlit.js
@@ -11,6 +11,7 @@ class NSlitSimulation extends Simulation {
         this.slitWidth = slitWidth;
         this.slitSeparation = slitSeparation;
         this.slits = slits;
+        this.envelope = 1;
         this.color = w2h(this.wavelength);
 
         this.t = 0;
@@ -26,6 +27,7 @@ class NSlitSimulation extends Simulation {
             this.slitWidth / this.xpx2m, this.slitSeparation / this.xpx2m, this.slits);
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
     }
 
     evaluate = (theta) => {
@@ -40,6 +42,16 @@ class NSlitSimulation extends Simulation {
         return this.cache[theta];
     }
 
+    evaluateEnvelope = (theta) => {
+        theta = Math.round(theta * 1_000_00) / 1_000_00;
+        if (theta in this.cacheEnvelope) return this.cacheEnvelope[theta];
+        let sine = Math.sin(theta);
+        let a = Math.PI * this.slit.width * this.xpx2m * sine / this.wavelength;
+        let tmp = Math.sin(a) / a;
+        this.cacheEnvelope[theta] = tmp * tmp;
+        return this.cacheEnvelope[theta];
+    }
+
     update = () => {
         this.t += this.dt;
 
@@ -48,6 +60,7 @@ class NSlitSimulation extends Simulation {
             this.screen.draw();
             this.slit.draw();
             this.plotIntensity();
+            if (this.envelope) this.plotEnvelope();
             this.redraw = false;
         } else this.c.clearRect(0, this.screen.y + 2.5, this.cvs.width, this.slit.y - this.screen.y - 5);
 
@@ -77,11 +90,25 @@ class NSlitSimulation extends Simulation {
         this.c.stroke();
     }
 
+    plotEnvelope = () => {
+        this.c.beginPath();
+        this.c.lineWidth = 1;
+        this.c.strokeStyle = "#FFFFFF";
+        for (let x = 0; x <= this.cvs.width; x++) {
+            const theta = Math.atan2((x - this.slit.x) * this.xpx2m, (this.slit.y - this.screen.y) * this.ypx2m);
+            const intensity =  this.evaluateEnvelope(theta) * this.cvs.height / 5;
+            if (x === 0) this.c.moveTo(x, this.screen.y - 5 - intensity);
+            else this.c.lineTo(x, this.screen.y - 5 - intensity);
+        }
+        this.c.stroke();
+    }
+
     displayMeasurements = () => {
         this.c.save();
         this.c.beginPath();
         this.c.moveTo(this.cvs.width * 0.9, this.slit.y);
         this.c.lineTo(this.cvs.width * 0.9, this.screen.y);
+        this.c.lineWidth = 3;
         this.c.strokeStyle = "#179e7e";
         this.c.stroke();
         this.c.translate(this.cvs.width * 0.9 + 40, (this.slit.y + this.screen.y) / 2);
@@ -98,6 +125,7 @@ class NSlitSimulation extends Simulation {
         this.color = w2h(wavelength);
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
     }
 
     setSlitWidth = (slitWidth) => {
@@ -105,6 +133,7 @@ class NSlitSimulation extends Simulation {
         this.slit.width = slitWidth / this.xpx2m;
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
     }
 
     setSlitSeparation = (slitSeparation) => {
@@ -112,6 +141,7 @@ class NSlitSimulation extends Simulation {
         this.slit.separation = slitSeparation / this.xpx2m;
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
     }
 
     setSlits = (slits) => {
@@ -119,6 +149,12 @@ class NSlitSimulation extends Simulation {
         this.slit.slits = slits;
         this.redraw = true;
         this.cache = {};
+        this.cacheEnvelope = {};
+    }
+
+    setEnvelope = (envelope) => {
+        this.envelope = envelope;
+        this.redraw = true;
     }
 
     intensityAt = (x, y) => {
diff --git a/src/simulations/double_slit_diffraction.md b/src/simulations/double_slit_diffraction.md
index 359c017..0ce0b2f 100644
--- a/src/simulations/double_slit_diffraction.md
+++ b/src/simulations/double_slit_diffraction.md
@@ -12,5 +12,9 @@
     <input type="range" min="380" max="780" step="10" value="500" class="slider" id="wavelengthInput_DS">
     Wavelength: <span id="wavelengthValue_DS">500</span> nm
 </div>
+<div class="envelope">
+    <input type="checkbox" id="envelopeInput_DS" checked="checked">
+    <label for="envelopeInput_DS">Toggle Envelope</label>
+</div>
 
 <script type="module" src="../javascript/sim5.js"></script>
\ No newline at end of file
diff --git a/src/simulations/n_slit_diffraction.md b/src/simulations/n_slit_diffraction.md
index 1419163..39c21ed 100644
--- a/src/simulations/n_slit_diffraction.md
+++ b/src/simulations/n_slit_diffraction.md
@@ -16,5 +16,9 @@
     <input type="range" min="380" max="780" step="10" value="500" class="slider" id="wavelengthInput_nSlit">
     Wavelength: <span id="wavelengthValue_nSlit">500</span> nm
 </div>
+<div class="envelope">
+    <input type="checkbox" id="envelopeInput_nSlit" checked="checked">
+    <label for="envelopeInput_nSlit">Toggle Envelope</label>
+</div>
 
 <script type="module" src="../javascript/sim6.js"></script>
\ No newline at end of file