diff --git a/src/fitter.rs b/src/fitter.rs
index ea67001..07eab9c 100644
--- a/src/fitter.rs
+++ b/src/fitter.rs
@@ -2,7 +2,7 @@ mod recursive;
 
 pub use recursive::Recursive;
 
-pub trait Fitter {
+pub trait Fitter: FitterClone {
     fn add_sample(&mut self, t: f64) -> usize;
 
     fn allocate(&mut self);
@@ -26,3 +26,22 @@ pub trait Fitter {
     fn ns(&self, idx: usize) -> f64;
     fn ns_mut(&mut self, idx: usize) -> &mut f64;
 }
+
+pub trait FitterClone {
+    fn clone_box(&self) -> Box<dyn Fitter>;
+}
+
+impl<T> FitterClone for T
+where
+    T: 'static + Fitter + Clone,
+{
+    fn clone_box(&self) -> Box<dyn Fitter> {
+        Box::new(self.clone())
+    }
+}
+
+impl Clone for Box<dyn Fitter> {
+    fn clone(&self) -> Box<dyn Fitter> {
+        self.clone_box()
+    }
+}
diff --git a/src/fitter/recursive.rs b/src/fitter/recursive.rs
index 2993dfb..5afef4d 100644
--- a/src/fitter/recursive.rs
+++ b/src/fitter/recursive.rs
@@ -81,7 +81,7 @@ impl<K: Kernel> fmt::Debug for Recursive<K> {
     }
 }
 
-impl<K: Kernel> Fitter for Recursive<K> {
+impl<K: 'static + Kernel + Clone> Fitter for Recursive<K> {
     fn add_sample(&mut self, t: f64) -> usize {
         let idx = self.ts.len() + self.ts_new.len();
 
diff --git a/src/item.rs b/src/item.rs
index c7b892b..53cfdb6 100644
--- a/src/item.rs
+++ b/src/item.rs
@@ -1,5 +1,6 @@
 use crate::fitter::Fitter;
 
+#[derive(Clone)]
 pub struct Item {
     pub fitter: Box<dyn Fitter>,
 }
diff --git a/src/kernel.rs b/src/kernel.rs
index 94cc591..a455be5 100644
--- a/src/kernel.rs
+++ b/src/kernel.rs
@@ -28,7 +28,7 @@ pub(crate) fn distance(ts1: &[f64], ts2: &[f64]) -> Array2<f64> {
     r
 }
 
-pub trait Kernel {
+pub trait Kernel: KernelClone {
     fn k_mat(&self, ts1: &[f64], ts2: Option<&[f64]>) -> Array2<f64>;
     fn k_diag(&self, ts: &[f64]) -> Array1<f64>;
     fn order(&self) -> usize;
@@ -41,6 +41,25 @@ pub trait Kernel {
     fn noise_cov(&self, t0: f64, t1: f64) -> Array2<f64>;
 }
 
+pub trait KernelClone {
+    fn clone_box(&self) -> Box<dyn Kernel>;
+}
+
+impl<T> KernelClone for T
+where
+    T: 'static + Kernel + Clone,
+{
+    fn clone_box(&self) -> Box<dyn Kernel> {
+        Box::new(self.clone())
+    }
+}
+
+impl Clone for Box<dyn Kernel> {
+    fn clone(&self) -> Box<dyn Kernel> {
+        self.clone_box()
+    }
+}
+
 impl Kernel for Vec<Box<dyn Kernel>> {
     fn k_mat(&self, ts1: &[f64], ts2: Option<&[f64]>) -> Array2<f64> {
         let n = ts1.len();
@@ -533,7 +552,7 @@ mod tests {
 
 macro_rules! tuple_impls {
     ( $( $name:ident )+ ) => {
-        impl<$($name: Kernel),+> Kernel for ($($name,)+) {
+        impl<$($name: 'static + Kernel + Clone),+> Kernel for ($($name,)+) {
             fn k_mat(&self, ts1: &[f64], ts2: Option<&[f64]>) -> Array2<f64> {
                 let n = ts1.len();
                 let m = ts2.map_or(n, |ts| ts.len());
diff --git a/src/kernel/affine.rs b/src/kernel/affine.rs
index 258b093..24aa578 100644
--- a/src/kernel/affine.rs
+++ b/src/kernel/affine.rs
@@ -2,6 +2,7 @@ use ndarray::prelude::*;
 
 use super::Kernel;
 
+#[derive(Clone, Copy)]
 pub struct Affine {
     var_offset: f64,
     var_slope: f64,
diff --git a/src/kernel/constant.rs b/src/kernel/constant.rs
index 1340e1f..0929c91 100644
--- a/src/kernel/constant.rs
+++ b/src/kernel/constant.rs
@@ -2,6 +2,7 @@ use ndarray::prelude::*;
 
 use super::Kernel;
 
+#[derive(Clone, Copy)]
 pub struct Constant {
     var: f64,
 }
diff --git a/src/kernel/exponential.rs b/src/kernel/exponential.rs
index cba50b0..4f9f87b 100644
--- a/src/kernel/exponential.rs
+++ b/src/kernel/exponential.rs
@@ -2,6 +2,7 @@ use ndarray::prelude::*;
 
 use super::Kernel;
 
+#[derive(Clone, Copy)]
 pub struct Exponential {
     var: f64,
     l_scale: f64,
diff --git a/src/kernel/matern32.rs b/src/kernel/matern32.rs
index cf63391..84af987 100644
--- a/src/kernel/matern32.rs
+++ b/src/kernel/matern32.rs
@@ -2,7 +2,7 @@ use ndarray::prelude::*;
 
 use super::Kernel;
 
-#[derive(Clone)]
+#[derive(Clone, Copy)]
 pub struct Matern32 {
     var: f64,
     l_scale: f64,
diff --git a/src/kernel/matern52.rs b/src/kernel/matern52.rs
index d4533e0..63376b9 100644
--- a/src/kernel/matern52.rs
+++ b/src/kernel/matern52.rs
@@ -2,6 +2,7 @@ use ndarray::prelude::*;
 
 use super::Kernel;
 
+#[derive(Clone, Copy)]
 pub struct Matern52 {
     var: f64,
     l_scale: f64,
diff --git a/src/kernel/wiener.rs b/src/kernel/wiener.rs
index 1a86d0a..025571b 100644
--- a/src/kernel/wiener.rs
+++ b/src/kernel/wiener.rs
@@ -2,6 +2,7 @@ use ndarray::prelude::*;
 
 use super::Kernel;
 
+#[derive(Clone, Copy)]
 pub struct Wiener {
     var: f64,
     t0: f64,
diff --git a/src/model/binary.rs b/src/model/binary.rs
index a3dadc4..0069be8 100644
--- a/src/model/binary.rs
+++ b/src/model/binary.rs
@@ -12,6 +12,7 @@ trait BinaryObeservation: Observation {
 }
 */
 
+#[derive(Clone, Copy)]
 pub enum Observation {
     Probit,
     Logit,
@@ -23,6 +24,7 @@ pub enum FitMethod {
     Kl,
 }
 
+#[derive(Clone)]
 pub struct Binary {
     pub storage: Storage,
     last_t: f64,
@@ -50,7 +52,7 @@ impl Binary {
         Self::new(Observation::Logit)
     }
 
-    pub fn add_item<K: Kernel + 'static>(&mut self, name: &str, kernel: K) {
+    pub fn add_item<K: Kernel + 'static + Clone>(&mut self, name: &str, kernel: K) {
         if self.storage.contains_key(name) {
             panic!("item '{}' already added", name);
         }
diff --git a/src/model/difference.rs b/src/model/difference.rs
index f7f0c28..1145503 100644
--- a/src/model/difference.rs
+++ b/src/model/difference.rs
@@ -12,6 +12,7 @@ pub enum DifferenceModelFitMethod {
     Kl,
 }
 
+#[derive(Clone)]
 pub struct DifferenceModel {
     storage: Storage,
     last_t: f64,
@@ -31,7 +32,7 @@ impl DifferenceModel {
         }
     }
 
-    pub fn add_item<K: Kernel + 'static>(&mut self, name: &str, kernel: K) {
+    pub fn add_item<K: Kernel + 'static + Clone>(&mut self, name: &str, kernel: K) {
         if self.storage.contains_key(name) {
             panic!("item '{}' already added", name);
         }
diff --git a/src/model/ternary.rs b/src/model/ternary.rs
index ea7411c..7dae213 100644
--- a/src/model/ternary.rs
+++ b/src/model/ternary.rs
@@ -18,6 +18,7 @@ pub enum FitMethod {
     Kl,
 }
 
+#[derive(Clone)]
 pub struct TernaryModel {
     storage: Storage,
     last_t: f64,
@@ -47,7 +48,7 @@ impl TernaryModel {
         Self::new(Observation::Logit, margin)
     }
 
-    pub fn add_item<K: Kernel + 'static>(&mut self, name: &str, kernel: K) {
+    pub fn add_item<K: Kernel + 'static + Clone>(&mut self, name: &str, kernel: K) {
         if self.storage.contains_key(name) {
             panic!("item '{}' already added", name);
         }
diff --git a/src/observation.rs b/src/observation.rs
index 11b3bda..2859b3b 100644
--- a/src/observation.rs
+++ b/src/observation.rs
@@ -6,11 +6,30 @@ mod ordinal;
 pub use gaussian::*;
 pub use ordinal::*;
 
-pub trait Observation {
+pub trait Observation: ObservationClone {
     fn ep_update(&mut self, storage: &mut Storage, lr: f64) -> f64;
     fn kl_update(&mut self, storage: &mut Storage, lr: f64) -> f64;
 }
 
+pub trait ObservationClone {
+    fn clone_box(&self) -> Box<dyn Observation>;
+}
+
+impl<T> ObservationClone for T
+where
+    T: 'static + Observation + Clone,
+{
+    fn clone_box(&self) -> Box<dyn Observation> {
+        Box::new(self.clone())
+    }
+}
+
+impl Clone for Box<dyn Observation> {
+    fn clone(&self) -> Box<dyn Observation> {
+        self.clone_box()
+    }
+}
+
 pub fn f_params(elems: &[(usize, f64)], t: f64, storage: &Storage) -> (f64, f64) {
     let mut m = 0.0;
     let mut v = 0.0;
@@ -25,6 +44,7 @@ pub fn f_params(elems: &[(usize, f64)], t: f64, storage: &Storage) -> (f64, f64)
     (m, v)
 }
 
+#[derive(Clone)]
 pub(crate) struct Core {
     pub m: usize,
     pub items: Vec<usize>,
diff --git a/src/observation/gaussian.rs b/src/observation/gaussian.rs
index 0185448..ea982e4 100644
--- a/src/observation/gaussian.rs
+++ b/src/observation/gaussian.rs
@@ -14,6 +14,7 @@ fn mm_gaussian(mean_cav: f64, var_cav: f64, diff: f64, var_obs: f64) -> (f64, f6
     (logpart, dlogpart, d2logpart)
 }
 
+#[derive(Clone)]
 pub struct GaussianObservation {
     core: Core,
     diff: f64,
diff --git a/src/observation/ordinal.rs b/src/observation/ordinal.rs
index a5885cb..5556f15 100644
--- a/src/observation/ordinal.rs
+++ b/src/observation/ordinal.rs
@@ -87,6 +87,7 @@ where
     (exp_ll, alpha, beta)
 }
 
+#[derive(Clone)]
 pub struct ProbitWinObservation {
     core: Core,
     margin: f64,
@@ -126,6 +127,7 @@ impl Observation for ProbitWinObservation {
     }
 }
 
+#[derive(Clone)]
 pub struct ProbitTieObservation {
     core: Core,
     margin: f64,
@@ -165,6 +167,7 @@ impl Observation for ProbitTieObservation {
     }
 }
 
+#[derive(Clone)]
 pub struct LogitWinObservation {
     core: Core,
     margin: f64,
@@ -197,6 +200,7 @@ impl Observation for LogitWinObservation {
     }
 }
 
+#[derive(Clone)]
 pub struct LogitTieObservation {
     core: Core,
     margin: f64,
diff --git a/src/storage.rs b/src/storage.rs
index 154c4de..48ce3ac 100644
--- a/src/storage.rs
+++ b/src/storage.rs
@@ -22,7 +22,7 @@ pub trait Backend {
 }
 */
 
-#[derive(Default)]
+#[derive(Clone, Default)]
 pub struct Storage {
     keys: HashMap<String, usize>,
     items: Vec<Item>,
diff --git a/tests/kickscore-basics.rs b/tests/kickscore-basics.rs
index b1d9753..9e9d1d6 100644
--- a/tests/kickscore-basics.rs
+++ b/tests/kickscore-basics.rs
@@ -35,9 +35,9 @@ fn kickscore_basic() {
 
     let (p_win, _p_los) = model.probabilities(&["Jerry"], &["Tom"], 2.0);
 
-    assert_abs_diff_eq!(p_win, 0.4455095363120037, epsilon = f64::EPSILON);
+    assert_abs_diff_eq!(p_win, 0.4705389648502623, epsilon = f64::EPSILON);
 
     let (p_win, _p_los) = model.probabilities(&["Jerry"], &["Tom"], -1.0);
 
-    assert_abs_diff_eq!(p_win, 0.9037560799725326, epsilon = f64::EPSILON);
+    assert_abs_diff_eq!(p_win, 0.7030407811954662, epsilon = f64::EPSILON);
 }
diff --git a/tests/nba-history.rs b/tests/nba-history.rs
index ac1aeb2..011153d 100644
--- a/tests/nba-history.rs
+++ b/tests/nba-history.rs
@@ -84,7 +84,7 @@ fn nba_history() {
             .unix_timestamp() as f64,
     );
 
-    assert_abs_diff_eq!(p_win, 0.9002599772490479, epsilon = f64::EPSILON);
+    assert_abs_diff_eq!(p_win, 0.8987931627209078, epsilon = f64::EPSILON);
 
     let (p_win, _) = model.probabilities(
         &["CHI"],
@@ -95,7 +95,7 @@ fn nba_history() {
             .unix_timestamp() as f64,
     );
 
-    assert_abs_diff_eq!(p_win, 0.22837870685441986, epsilon = f64::EPSILON);
+    assert_abs_diff_eq!(p_win, 0.22890824995747874, epsilon = f64::EPSILON);
 
     let (p_win, _) = model.probabilities(
         &["CHI"],