diff --git a/Cargo.toml b/Cargo.toml
index c70de2d..8d0e315 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,7 +7,6 @@ license = "MIT OR Apache-2.0"
 
 [dependencies]
 cblas = "0.2"
-derivative = "2.1"
 lapacke = "0.2"
 ndarray = "0.13"
 ordered-float = "1.0"
diff --git a/src/fitter/recursive.rs b/src/fitter/recursive.rs
index f0d7c69..1b107a7 100644
--- a/src/fitter/recursive.rs
+++ b/src/fitter/recursive.rs
@@ -1,4 +1,6 @@
-use derivative::Derivative;
+use std::fmt;
+
+// use derivative::Derivative;
 use ndarray::prelude::*;
 use ndarray::stack;
 
@@ -6,11 +8,8 @@ use crate::kernel::Kernel;
 
 use super::Fitter;
 
-#[derive(Derivative)]
-#[derivative(Debug)]
 pub struct RecursiveFitter {
     ts_new: Vec<f64>,
-    #[derivative(Debug = "ignore")]
     kernel: Box<dyn Kernel>,
     ts: Vec<f64>,
     ms: ArrayD<f64>, // TODO Replace with a vec
@@ -58,6 +57,30 @@ impl RecursiveFitter {
     }
 }
 
+impl fmt::Debug for RecursiveFitter {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RecursiveFitter")
+            .field("ts_new", &self.ts_new)
+            .field("ts", &self.ts)
+            .field("ms", &self.ms)
+            .field("vs", &self.vs)
+            .field("ns", &self.ns)
+            .field("xs", &self.xs)
+            .field("is_fitted", &self.is_fitted)
+            .field("h", &self.h)
+            .field("i", &self.i)
+            .field("a", &self.a)
+            .field("q", &self.q)
+            .field("m_p", &self.m_p)
+            .field("p_p", &self.p_p)
+            .field("m_f", &self.m_f)
+            .field("p_f", &self.p_f)
+            .field("m_s", &self.m_s)
+            .field("p_s", &self.p_s)
+            .finish()
+    }
+}
+
 impl Fitter for RecursiveFitter {
     fn add_sample(&mut self, t: f64) -> usize {
         let idx = self.ts.len() + self.ts_new.len();
@@ -146,8 +169,6 @@ impl Fitter for RecursiveFitter {
             let k = self.p_p[i].dot(&self.h)
                 / (1.0 + self.xs[i] * self.h.dot(&self.p_p[i]).dot(&self.h));
 
-            // let k = Array1::from(k);
-
             self.m_f[i] =
                 &self.m_p[i] + &(&k * (self.ns[i] - self.xs[i] * self.h.dot(&self.m_p[i])));