diff --git a/rtchallenge/examples/eoc4.rs b/rtchallenge/examples/eoc4.rs
index 2df200c..43281c5 100644
--- a/rtchallenge/examples/eoc4.rs
+++ b/rtchallenge/examples/eoc4.rs
@@ -24,7 +24,7 @@ fn main() -> Result<()> {
     let w = 200;
     let h = w;
     let mut c = Canvas::new(w, h);
-    let t = Matrix4x4::translate(0., 0.75, 0.);
+    let t = Matrix4x4::translate(0., 0.4, 0.);
     let p = Tuple::point(0., 0., 0.);
     let rot_hour = Matrix4x4::rotation_z(-PI / 6.);
 
@@ -33,11 +33,14 @@ fn main() -> Result<()> {
     let h = h as f32;
     let h_w = w / 2.0;
     let h_h = h / 2.0;
+    // The 'world' exists between -0.5 - 0.5 in X-Y plane.
+    // To convert to screen space, we translate by 0.5, scale to canvas size,
+    // and invert the Y-axis.
+    let world_to_screen =
+        Matrix4x4::scaling(w as f32, -h as f32, 1.0) * Matrix4x4::translate(0.5, -0.5, 0.);
     for _ in 0..12 {
-        let x = (h_w + h_w * p.x) as usize;
-        // Y-axis is 0 at the top, and h at the bottom, flip it.
-        let y = (h - (h_h + h_h * p.y)) as usize;
-        draw_dot(&mut c, x, y);
+        let canvas_pixel = world_to_screen * p;
+        draw_dot(&mut c, canvas_pixel.x as usize, canvas_pixel.y as usize);
         p = rot_hour * p;
     }