diff --git a/Chapter03/Cargo.toml b/Chapter03/Cargo.toml
index a79cb18..eca4514 100644
--- a/Chapter03/Cargo.toml
+++ b/Chapter03/Cargo.toml
@@ -6,3 +6,6 @@ version = "1.0.0"
 floating-duration = "0.1.2"
 termion = "1.0"
 timebomb = "0.1"
+serde = "1.0"
+serde_json = "1.0"
+serde_derive = "1.0"
diff --git a/Chapter03/src/lib.rs b/Chapter03/src/lib.rs
index 2a4dcca..1e7fc06 100644
--- a/Chapter03/src/lib.rs
+++ b/Chapter03/src/lib.rs
@@ -4,6 +4,9 @@ mod motor;
 use physics::{ElevatorSpecification, ElevatorState, MotorInput, simulate_elevator, DataRecorder, MotorController, MotorVoltage};
 use motor::{SmoothMotorController};
 
+#[macro_use] extern crate serde_derive;
+extern crate serde;
+extern crate serde_json;
 extern crate floating_duration;
 use std::time::Instant;
 use std::env;
@@ -53,6 +56,7 @@ struct SimpleDataRecorder<'a, W: 'a + Write>
    termwidth: u64,
    termheight: u64,
    stdout: &'a mut raw::RawTerminal<W>,
+   log: File,
    record_location: Vec<f64>,
    record_velocity: Vec<f64>,
    record_acceleration: Vec<f64>,
@@ -62,10 +66,14 @@ impl<'a, W: Write> DataRecorder for SimpleDataRecorder<'a, W>
 {
    fn init(&mut self, esp: ElevatorSpecification, est: ElevatorState)
    {
-      self.esp = esp;
+      self.esp = esp.clone();
+      self.log.write_all(serde_json::to_string(&esp.clone()).unwrap().as_bytes()).expect("write spec to log");
    }
    fn poll(&mut self, est: ElevatorState, dst: u64)
    {
+      let datum = (est.clone(), dst);
+      self.log.write_all(serde_json::to_string(&datum).unwrap().as_bytes()).expect("write state to log");
+
       //5.4. Print realtime statistics
       print!("{}{}{}", clear::All, cursor::Goto(1, 1), cursor::Hide);
       let carriage_floor = (est.location / self.esp.floor_height).floor();
@@ -123,7 +131,7 @@ pub fn run_simulation()
    //1. Store location, velocity, and acceleration state
    //2. Store motor input voltage
    let mut est = ElevatorState {
-      timestamp: Instant::now(),
+      timestamp: 0.0,
       location: 0.0,
       velocity: 0.0,
       acceleration: 0.0,
@@ -198,13 +206,14 @@ pub fn run_simulation()
       termwidth: termsize.map(|(w,_)| w-2).expect("termwidth") as u64,
       termheight: termsize.map(|(_,h)| h-2).expect("termheight") as u64,
       stdout: &mut io::stdout().into_raw_mode().unwrap(),
+      log: File::create("simulation.log").expect("log file"),
       record_location: Vec::new(),
       record_velocity: Vec::new(),
       record_acceleration: Vec::new(),
       record_voltage: Vec::new()
    };
    let mut mc = SmoothMotorController {
-      timestamp: Instant::now(),
+      timestamp: 0.0,
       esp: esp.clone()
    };
 
diff --git a/Chapter03/src/motor.rs b/Chapter03/src/motor.rs
index 23eac07..2ab7509 100644
--- a/Chapter03/src/motor.rs
+++ b/Chapter03/src/motor.rs
@@ -76,7 +76,7 @@ impl MotorController for SimpleMotorController
 pub struct SmoothMotorController
 {
    pub esp: ElevatorSpecification,
-   pub timestamp: Instant
+   pub timestamp: f64
 }
 
 impl MotorController for SmoothMotorController
@@ -130,8 +130,8 @@ impl MotorController for SmoothMotorController
          let going_up = est.location < (dst as f64)*self.esp.floor_height;
 
          //time elapsed since last poll
-         let dt = est.timestamp.duration_since(self.timestamp)
-                     .as_fractional_secs();
+         let dt = est.timestamp - self.timestamp;
+         self.timestamp = est.timestamp;
 
          //Do not exceed maximum velocity
          if est.velocity.abs() >= MAX_VELOCITY {
diff --git a/Chapter03/src/physics.rs b/Chapter03/src/physics.rs
index 1080a11..0e0cff5 100644
--- a/Chapter03/src/physics.rs
+++ b/Chapter03/src/physics.rs
@@ -3,14 +3,14 @@ use std::time::Instant;
 use floating_duration::{TimeAsFloat, TimeFormat};
 use std::{thread, time};
 
-#[derive(Clone)]
+#[derive(Clone,Serialize,Deserialize)]
 pub enum MotorInput
 {
    Up { voltage: f64 },
    Down { voltage: f64 }
 }
 
-#[derive(Clone)]
+#[derive(Clone,Serialize,Deserialize)]
 pub struct ElevatorSpecification
 {
    pub floor_count: u64,
@@ -18,10 +18,10 @@ pub struct ElevatorSpecification
    pub carriage_weight: f64
 }
 
-#[derive(Clone)]
+#[derive(Clone,Serialize,Deserialize)]
 pub struct ElevatorState
 {
-   pub timestamp: Instant,
+   pub timestamp: f64,
    pub location: f64,
    pub velocity: f64,
    pub acceleration: f64,
@@ -81,13 +81,15 @@ pub fn simulate_elevator<MC: MotorController, DR: DataRecorder>(esp: ElevatorSpe
    dr.init(esp.clone(), est.clone());
 
    //5. Loop while there are remaining floor requests
+   let original_ts = Instant::now();
    while req.len() > 0
    {
       //5.1. Update location, velocity, and acceleration
       let now = Instant::now();
-      let dt = now.duration_since(est.timestamp)
+      let ts = now.duration_since(original_ts)
                   .as_fractional_secs();
-      est.timestamp = now;
+      let dt = ts - est.timestamp;
+      est.timestamp = ts;
 
       est.location = est.location + est.velocity * dt;
       est.velocity = est.velocity + est.acceleration * dt;