Adjust the values of [math]r[/math], [math]\theta[/math], [math]z[/math], [math]\Delta r[/math], [math]\Delta\theta[/math], and [math]\Delta z[/math] to see how the small cylindrical volume changes. Note that this volume has approximate dimensions [math]\Delta r \times (r\Delta\theta) \times \Delta z= r\Delta r\Delta\theta\Delta z[/math].