diff --git a/examples/coremem.rs b/examples/coremem.rs
index 686aa3f..71788c0 100644
--- a/examples/coremem.rs
+++ b/examples/coremem.rs
@@ -1,14 +1,19 @@
 use coremem::SimState;
 use coremem::render::NumericTermRenderer;
+use coremem::consts;
 use std::{thread, time};
 
 fn main() {
     let mut state = SimState::new(16);
+    state.impulse_b(0, 1.0/consts::C);
     state.impulse_e(0, 1.0);
+    state.impulse_b(7, 1.0/consts::C);
+    state.impulse_e(7, 1.0);
+    state.impulse_b(15, 1.0/consts::C);
     state.impulse_e(15, 1.0);
     loop {
         NumericTermRenderer.render(&state);
         state.step();
-        thread::sleep(time::Duration::from_millis(500));
+        thread::sleep(time::Duration::from_millis(100));
     }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 437a5b6..e258955 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,7 +14,7 @@ pub mod render;
 // mu_0 = vacuum permeability = 1.25663706212(19)×10−6 H/m
 // c_0 = speed of light in vacuum = 299792458
 
-mod consts {
+pub mod consts {
     /// Speed of light in a vacuum; m/s.
     /// Also equal to 1/sqrt(epsilon_0 mu_0)
     pub const C: f32 = 299792458f32;
@@ -57,6 +57,10 @@ impl SimState {
         self.cells[idx].ez += e;
     }
 
+    pub fn impulse_b(&mut self, idx: usize, y: f32) {
+        self.cells[idx].by += y;
+    }
+
     pub fn cells(&self) -> &[Cell] {
         &*self.cells
     }
diff --git a/src/render.rs b/src/render.rs
index 00e61db..fd305d6 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -4,14 +4,14 @@ pub struct NumericTermRenderer;
 
 impl NumericTermRenderer {
     pub fn render(&self, state: &SimState) {
-        print!("E:");
-        for cell in state.cells() {
-            print!("{:>10.1e} ", cell.ez());
-        }
-        print!("\nB:      ");
+        print!("B:      ");
         for cell in state.cells() {
             print!("{:>10.1e} ", cell.by());
         }
+        print!("\nE:");
+        for cell in state.cells() {
+            print!("{:>10.1e} ", cell.ez());
+        }
         print!("\n");
     }
 }