diff --git a/src/main.rs b/src/main.rs
index 52914baaaa0e0ba62b8e5168350e915574d1a078..c1dac899433039de335ac97875811ddba959a359 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,11 +2,11 @@ use anyhow::bail;
 use image::{GenericImageView, ImageReader};
 
 const TOAST_TIME_SECONDS: u64 = 60;
-const CENTER_X: u32 = 100;
-const CENTER_Y: u32 = 100;
-const BREAD_HEIGHT: f64 = 15.5;
+const CENTER_X: f64 = 100.0;
+const CENTER_Y: f64 = 100.0;
+const BREAD_HEIGHT: f64 = 15.3;
 const IDLE_HEIGHT: f64 = BREAD_HEIGHT + 10.0;
-const PIXEL_SIZE_MM: f64 = 2.0;
+const PIXEL_SIZE_MM: f64 = 4.0;
 
 fn main() -> anyhow::Result<()> {
     let img = ImageReader::open("/home/stephen/Downloads/qr_tiny.png")?.decode()?;
@@ -22,7 +22,10 @@ fn main() -> anyhow::Result<()> {
                     // nothing, for now
                 }
                 [255, 255, 255, 255] => {
-                    toast(x, y);
+                    toast(
+                        x as f64 - (img.width() as f64 / 2.0),
+                        y as f64 - (img.height() as f64 / 2.0),
+                    );
                 }
                 _ => bail!("Pixel was not entirely black nor entirely white: {:?}", p),
             }
@@ -36,15 +39,15 @@ fn preamble() {
     println!(
         r#"
 G28 ; home
-M109 S220 ; heat hotend to 220C and wait
 G90 ; absolute positioning
 G0 Z{IDLE_HEIGHT}
 G0 X{CENTER_X} Y{CENTER_Y}
+M109 S220 ; heat hotend to 220C and wait
 "#
     );
 }
 
-fn toast(x: u32, y: u32) {
+fn toast(x: f64, y: f64) {
     println!(
         r#"
 G0 X{:.2} Y{:.2};
@@ -52,7 +55,7 @@ G0 Z{BREAD_HEIGHT};
 G4 S{TOAST_TIME_SECONDS} ; wait
 G0 Z{IDLE_HEIGHT};
 "#,
-        x as f64 * PIXEL_SIZE_MM,
-        y as f64 * PIXEL_SIZE_MM
+        x * PIXEL_SIZE_MM + CENTER_X,
+        y * PIXEL_SIZE_MM + CENTER_Y
     );
 }