diff --git a/src/services/gesture_service/gesture_service.js b/src/services/gesture_service/gesture_service.js
index 2e39003c8c..efc0ca78f7 100644
--- a/src/services/gesture_service/gesture_service.js
+++ b/src/services/gesture_service/gesture_service.js
@@ -10,11 +10,14 @@ const touchEventCoord = e => ([e.touches[0].screenX, e.touches[0].screenY])
 
 const vectorLength = v => Math.sqrt(v[0] * v[0] + v[1] * v[1])
 
-const perpendicular = v => [v[1], v[0]]
+const perpendicular = v => [v[1], -v[0]]
 
 const dotProduct = (v1, v2) => v1[0] * v2[0] + v1[1] * v2[1]
 
-const vectorFlatten = (v1, v2) => [v1[0] * v2[0], v1[1] * v2[1]]
+const project = (v1, v2) => {
+  const scalar = (dotProduct(v1, v2) / dotProduct(v2, v2))
+  return [scalar * v2[0], scalar * v2[1]]
+}
 
 // direction: either use the constants above or an arbitrary 2d vector.
 // threshold: how many Px to move from touch origin before checking if the
@@ -46,12 +49,12 @@ const updateSwipe = (event, gesture) => {
   // movement is opposite from direction
   if (dotProduct(delta, gesture.direction) < 0) return
   // movement perpendicular to direction is too much
-  const towardsDir = vectorFlatten(gesture.direction, delta)
+  const towardsDir = project(delta, gesture.direction)
   const perpendicularDir = perpendicular(gesture.direction)
-  const towardsPerpendicular = vectorFlatten(perpendicularDir, delta)
+  const towardsPerpendicular = project(delta, perpendicularDir)
   if (
-    vectorLength(towardsDir) <
-    gesture.perpendicularTolerance * vectorLength(towardsPerpendicular)
+    vectorLength(towardsDir) * gesture.perpendicularTolerance <
+    vectorLength(towardsPerpendicular)
   ) return
 
   gesture.onSwipe()
diff --git a/test/unit/specs/services/gesture_service/gesture_service.spec.js b/test/unit/specs/services/gesture_service/gesture_service.spec.js
new file mode 100644
index 0000000000..4a1b009a25
--- /dev/null
+++ b/test/unit/specs/services/gesture_service/gesture_service.spec.js
@@ -0,0 +1,120 @@
+import GestureService from 'src/services/gesture_service/gesture_service.js'
+
+const mockTouchEvent = (x, y) => ({
+  touches: [
+    {
+      screenX: x,
+      screenY: y
+    }
+  ]
+})
+
+describe.only('GestureService', () => {
+  describe('swipeGesture', () => {
+    it('calls the callback on a successful swipe', () => {
+      let swiped = false
+      const callback = () => { swiped = true }
+      const gesture = GestureService.swipeGesture(
+        GestureService.DIRECTION_RIGHT,
+        callback
+      )
+
+      GestureService.beginSwipe(mockTouchEvent(100, 100), gesture)
+      GestureService.updateSwipe(mockTouchEvent(200, 100), gesture)
+
+      expect(swiped).to.eql(true)
+    })
+
+    it('calls the callback only once per begin', () => {
+      let hits = 0
+      const callback = () => { hits += 1 }
+      const gesture = GestureService.swipeGesture(
+        GestureService.DIRECTION_RIGHT,
+        callback
+      )
+
+      GestureService.beginSwipe(mockTouchEvent(100, 100), gesture)
+      GestureService.updateSwipe(mockTouchEvent(150, 100), gesture)
+      GestureService.updateSwipe(mockTouchEvent(200, 100), gesture)
+
+      expect(hits).to.eql(1)
+    })
+
+    it('doesn\'t call the callback on an opposite swipe', () => {
+      let swiped = false
+      const callback = () => { swiped = true }
+      const gesture = GestureService.swipeGesture(
+        GestureService.DIRECTION_RIGHT,
+        callback
+      )
+
+      GestureService.beginSwipe(mockTouchEvent(100, 100), gesture)
+      GestureService.updateSwipe(mockTouchEvent(0, 100), gesture)
+
+      expect(swiped).to.eql(false)
+    })
+
+    it('doesn\'t call the callback on a swipe below threshold', () => {
+      let swiped = false
+      const callback = () => { swiped = true }
+      const gesture = GestureService.swipeGesture(
+        GestureService.DIRECTION_RIGHT,
+        callback,
+        100
+      )
+
+      GestureService.beginSwipe(mockTouchEvent(100, 100), gesture)
+      GestureService.updateSwipe(mockTouchEvent(150, 100), gesture)
+
+      expect(swiped).to.eql(false)
+    })
+
+    it('doesn\'t call the callback on a perpendicular swipe', () => {
+      let swiped = false
+      const callback = () => { swiped = true }
+      const gesture = GestureService.swipeGesture(
+        GestureService.DIRECTION_RIGHT,
+        callback,
+        30,
+        0.5
+      )
+
+      GestureService.beginSwipe(mockTouchEvent(100, 100), gesture)
+      GestureService.updateSwipe(mockTouchEvent(150, 200), gesture)
+
+      expect(swiped).to.eql(false)
+    })
+
+    it('calls the callback on perpendicular swipe if within tolerance', () => {
+      let swiped = false
+      const callback = () => { swiped = true }
+      const gesture = GestureService.swipeGesture(
+        GestureService.DIRECTION_RIGHT,
+        callback,
+        30,
+        2.0
+      )
+
+      GestureService.beginSwipe(mockTouchEvent(100, 100), gesture)
+      GestureService.updateSwipe(mockTouchEvent(150, 150), gesture)
+
+      expect(swiped).to.eql(true)
+    })
+
+    it('works with any arbitrary 2d directions', () => {
+      let swiped = false
+      const callback = () => { swiped = true }
+      const gesture = GestureService.swipeGesture(
+        [-1, -1],
+        callback,
+        30,
+        0.1
+      )
+
+      GestureService.beginSwipe(mockTouchEvent(100, 100), gesture)
+      GestureService.updateSwipe(mockTouchEvent(60, 60), gesture)
+
+      expect(swiped).to.eql(true)
+    })
+  })
+})