diff --git a/lib/growth/calc/centile.ex b/lib/growth/calc/centile.ex
index 91c6ba6..3acd78c 100644
--- a/lib/growth/calc/centile.ex
+++ b/lib/growth/calc/centile.ex
@@ -1,18 +1,39 @@
 defmodule Growth.Calc.Centile do
   @moduledoc """
-    measures =
-      [
-        [30, -1.7862, 16.9392, 0.1107],
-        [14, -1.3592, 20.4951, 0.12579],
-        [19, -1.6318, 16.049, 0.10038]
-      ]
-    Enum.map(measures, &apply(Growth.Calc.Centile, :compute, &1))
+  Calculate percentile for a given measurement and the fitted values of Box-Cox by age/height:
+
+  * power
+  * median
+  * coefficientof variation
+
+  This calculation is described in the [instructions provided by the World Health Organization](https://cdn.who.int/media/docs/default-source/child-growth/growth-reference-5-19-years/computation.pdf).
+
+  ## Examples:
+
+      iex> measures =
+      ...>   [
+      ...>     [30, -1.7862, 16.9392, 0.1107],
+      ...>     [14, -1.3592, 20.4951, 0.12579],
+      ...>     [19, -1.6318, 16.049, 0.10038]
+      ...>   ]
+      iex> Enum.map(measures, &apply(Growth.Calc.Centile, :compute, &1))
+      [:na, :na, 19.0]
+
   """
 
   alias Growth.Calc.ZScore
 
-  # TODO: (jpd) add documentation and typespecs
+  @spec compute(number(), number(), number(), number()) :: number()
+  @doc """
+  Compute the centile for a given measurement (`y`) and the Box-Cox values: power (`l`), median (`m`), and
+  coefficient of variation (`s`).
 
+  ## Examples:
+
+      iex> Growth.Calc.Centile.compute(19, -1.6318, 16.049, 0.10038)
+      19.0
+
+  """
   def compute(y, l, m, s) do
     zscore = ZScore.raw(y, l, m, s)
 
diff --git a/lib/growth/calc/z_score.ex b/lib/growth/calc/z_score.ex
index 540214f..48a9961 100644
--- a/lib/growth/calc/z_score.ex
+++ b/lib/growth/calc/z_score.ex
@@ -1,26 +1,70 @@
 defmodule Growth.Calc.ZScore do
   @moduledoc """
-    measures =
-      [
-        [30, -1.7862, 16.9392, 0.1107],
-        [14, -1.3592, 20.4951, 0.12579],
-        [19, -1.6318, 16.049, 0.10038]
-      ]
-    Enum.map(measures, &apply(Growth.Calc.ZScore, :compute, &1))
+  Calculate z-score for a given measurement and the fitted values of Box-Cox by age/height:
+
+  * power
+  * median
+  * coefficientof variation
+
+  This calculation is described in the [instructions provided by the World Health Organization](https://cdn.who.int/media/docs/default-source/child-growth/growth-reference-5-19-years/computation.pdf).
+
+  ## Examples:
+
+      iex> measures =
+      ...>   [
+      ...>     [30, -1.7862, 16.9392, 0.1107],
+      ...>     [14, -1.3592, 20.4951, 0.12579],
+      ...>     [19, -1.6318, 16.049, 0.10038]
+      ...>   ]
+      iex> Enum.map(measures, &apply(Growth.Calc.ZScore, :compute, &1))
+      [3.35390255606726, -3.7985108865993493, 1.4698319520484722]
+
   """
 
-  # TODO: (jpd) add documentation and typespecs
+  @spec compute(number(), number(), number(), number()) :: number()
+  @doc """
+  Compute the adjusted z-score for a given measurement (`y`) and the Box-Cox values: power (`l`), median (`m`), and
+  coefficient of variation (`s`).
 
+  ## Examples:
+
+      iex> Growth.Calc.ZScore.compute(30, -1.7862, 16.9392, 0.1107)
+      3.35390255606726
+      iex> Growth.Calc.ZScore.compute(14, -1.3592, 20.4951, 0.12579)
+      -3.7985108865993493
+      iex> Growth.Calc.ZScore.compute(19, -1.6318, 16.049, 0.10038)
+      1.4698319520484722
+
+  """
   def compute(y, l, m, s) do
     y
     |> raw(l, m, s)
     |> adjust(y, l, m, s)
   end
 
+  @spec raw(number(), number(), number(), number()) :: number()
+  @doc """
+  Compute the raw z-score for a given measurement (`y`) and the Box-Cox values, power (`l`), median (`m`), and
+  coefficient of variation (`s`).
+
+  ## Examples
+
+      iex> Growth.Calc.ZScore.raw(30, -1.7862, 16.9392, 0.1107)
+      3.2353902101095855
+      iex> Growth.Calc.ZScore.raw(14, -1.3592, 20.4951, 0.12579)
+      -3.969714730727475
+      iex> Growth.Calc.ZScore.compute(19, -1.6318, 16.049, 0.10038)
+      1.4698319520484722
+
+  """
   def raw(y, l, m, s) do
     (:math.pow(y / m, l) - 1) / (s * l)
   end
 
+  @spec adjust(number(), number(), number(), number(), number()) :: number()
+  @doc """
+  Adjust the raw z-score considering that extreme values, beyond -3 and 3 standard deviation, must be handled differently.
+  """
   def adjust(zscore, y, l, m, s) when zscore > 3 do
     [sd2, sd3, _, _] = cutoffs(l, m, s)
     sd_delta = sd3 - sd2
@@ -37,11 +81,23 @@ defmodule Growth.Calc.ZScore do
     zscore
   end
 
+  @spec cutoffs(number(), number(), number()) :: [number()]
+  @doc """
+  Calculate the standard deviations cutoffs (2, 3, -2, and -3) for a given set of fitted Box-Cox values: power (`l`),
+  median (`m`), and coefficient of variation (`s`).
+
+  These cutoffs are used to calculate the adjusted z-score.
+  """
   def cutoffs(l, m, s) do
-    Enum.map([2, 3, -2, -3], &cutoff_for_standard_deviation(&1, l, m, s))
+    Enum.map([2, 3, -2, -3], &measure_at_standard_deviation(&1, l, m, s))
   end
 
-  def cutoff_for_standard_deviation(sd, l, m, s) do
+  @spec measure_at_standard_deviation(integer(), number(), number(), number()) :: number()
+  @doc """
+  Calculate the measure value at a given standard deviation (`sd`), considering the fitted Box-Cox values: power (`l`),
+  median (`m`), and coefficient of variation (`s`).
+  """
+  def measure_at_standard_deviation(sd, l, m, s) do
     m * :math.pow(1 + l * s * sd, 1 / l)
   end
 end