diff --git a/src/analog.rs b/src/analog.rs
index 7c73435..ef16c8c 100644
--- a/src/analog.rs
+++ b/src/analog.rs
@@ -8,6 +8,7 @@ use crate::processor::Processor;
 use crate::{C3dParseError, C3dWriteError};
 use grid::Grid;
 
+/// Analog format describes whether the analog data is signed or unsigned.
 #[derive(Debug, Clone, PartialEq, Default)]
 pub enum AnalogFormat {
     #[default]
@@ -35,6 +36,7 @@ impl AnalogFormat {
     }
 }
 
+/// An offset that is subtracted from the analog data before scaling.
 #[derive(Debug, Clone, PartialEq)]
 pub enum AnalogOffset {
     Signed(Vec<i16>),
@@ -68,9 +70,11 @@ impl AnalogOffset {
     }
 }
 
+/// Analog data and parameters are stored as a struct.
+/// Definitions for data and parameters are from the C3D file format documentation.
 #[derive(Debug, Clone)]
 pub struct Analog {
-    pub parsed_header: bool,
+    parsed_header: bool,
     pub analog: Grid<f64>,
     pub labels: Vec<String>,
     pub descriptions: Vec<String>,
diff --git a/src/data.rs b/src/data.rs
index 65c6398..850073f 100644
--- a/src/data.rs
+++ b/src/data.rs
@@ -2,6 +2,9 @@
 use crate::C3dParseError;
 use std::ops::{Deref, DerefMut};
 
+/// DataFormat is the format of the data in the file.
+/// Floating point data is larger than integer data, but the loss of precision
+/// in integer data may be acceptable for some applications.
 #[derive(Debug, Clone, PartialEq, Default)]
 pub enum DataFormat {
     #[default]
@@ -30,6 +33,9 @@ pub(crate) fn get_analog_bytes_per_frame(
     Ok(bytes_per_analog_point * analog_samples_per_frame as usize)
 }
 
+/// MarkerPoint contains both the points and residuals for a marker.
+/// The residuals are the average distance between the marker and the reconstructed point.
+/// Cameras is a bitfield of which cameras saw the marker.
 #[derive(Debug, Clone, Copy, PartialEq, Default)]
 pub struct MarkerPoint {
     pub point: [f32; 3],
@@ -72,6 +78,7 @@ impl MarkerPoint {
         *self
     }
 
+    /// used for writing to file
     pub(crate) fn cameras_as_byte(&self) -> u8 {
         let mut cameras_byte = 0;
         for (i, camera) in self.cameras.iter().enumerate() {
diff --git a/src/file_formats/sto.rs b/src/file_formats/sto.rs
index 1282630..e267c25 100644
--- a/src/file_formats/sto.rs
+++ b/src/file_formats/sto.rs
@@ -1,8 +1,11 @@
+//! STO file formats are used by OpenSim to store table-based data such as joint angles, muscle activations, and muscle forces.
+//! They can be used to store ground reaction forces/moments and emg data as well.
 use crate::{C3d, C3dWriteError};
 use std::io::Write;
 use std::path::PathBuf;
 use grid::Grid;
 
+/// The STO struct contains the data for writing an STO file.
 #[derive(Debug, Clone)]
 pub struct Sto {
     pub file_description: Option<String>,
diff --git a/src/file_formats/trc.rs b/src/file_formats/trc.rs
index 541e147..77cd9e8 100644
--- a/src/file_formats/trc.rs
+++ b/src/file_formats/trc.rs
@@ -1,3 +1,5 @@
+//! TRC file format is a Motion Analysis Corporation file format for storing 3D marker data.
+//! It is also used by OpenSim to store marker data.
 use crate::C3d;
 use crate::C3dWriteError;
 use std::io::Write;
@@ -6,6 +8,7 @@ use std::path::PathBuf;
 use crate::data::MarkerPoint;
 use grid::Grid;
 
+/// The TRC struct contains the data for writing a TRC file.
 #[derive(Debug, Clone)]
 pub struct Trc {
     pub path_file_type: u8,
diff --git a/tests/data/short-copy.c3d b/tests/data/short-copy.c3d
index 5270e8a..a625244 100644
Binary files a/tests/data/short-copy.c3d and b/tests/data/short-copy.c3d differ