diff --git a/gyro.py b/gyro.py
index 7396cb2..57f3b8b 100644
--- a/gyro.py
+++ b/gyro.py
@@ -100,6 +100,17 @@ class GyroVector:
         cAdd, cGyr = MobiusAddGyr(gA.cPos, gB.cPos)
         return GyroVector(cAdd, gA.cRot * gB.cRot * cGyr)
 
+    def __iadd__(self, gA):
+        cAdd, cGyr = MobiusAddGyr(self.cPos, gA.cPos)
+        self.cPos = cAdd
+        self.cRot = self.cRot * gA.cRot * cGyr
+
+    def __isub__(self, gA):
+        ngA = -gA
+        cAdd, cGyr = MobiusAddGyr(self.cPos, ngA.cPos)
+        self.cPos = cAdd
+        self.cRot = self.cRot * ngA.cRot * cGyr
+
     def __neg__(self):
         return GyroVector(-(self.cRot * self.cPos), 1/self.cRot)