diff --git a/08-Designing-Kalman-Filters.ipynb b/08-Designing-Kalman-Filters.ipynb
index 1805f1d..80a1247 100644
--- a/08-Designing-Kalman-Filters.ipynb
+++ b/08-Designing-Kalman-Filters.ipynb
@@ -2151,7 +2151,7 @@
     "\n",
     "To make it clearer, suppose that the wheel reports not position but the number of rotations of the wheels, where 1 revolution yields 2 meters of travel. In that case we would write\n",
     "\n",
-    "$$ \\begin{bmatrix}z_{wheel} \\\\ z_{ps}\\end{bmatrix} = \\begin{bmatrix}0.5 &0 \\\\ 1& 0\\end{bmatrix} \\begin{bmatrix}x \\\\ \\dot x\\end{bmatrix}$$\n",
+    "$$ \\begin{bmatrix}z_{rot} \\\\ z_{ps}\\end{bmatrix} = \\begin{bmatrix}0.5 &0 \\\\ 1& 0\\end{bmatrix} \\begin{bmatrix}x \\\\ \\dot x\\end{bmatrix}$$\n",
     "\n",
     "Now we have to design the measurement noise matrix $\\mathbf R$. Suppose that the measurement variance for the position is twice the variance of the wheel, and the standard deviation of the wheel is 1.5 meters. That gives us\n",
     "\n",