diff --git a/README.md b/README.md
index d4428a2..3382732 100644
--- a/README.md
+++ b/README.md
@@ -9,9 +9,10 @@ for decoding signals from various scientific and academic sattelites.
 * CMake ( > 3.1)
 * G++ (with C++11 support)
 * VOLK
-* libogg 
+* libogg
 * libvorbis
 * libpng
+* libpng++
 * git
 
 **Optional**
@@ -34,12 +35,12 @@ If this is the first time you are building the gr-satnogs module run
 By default, the **SatNOGS** module will use the default installation prefix.
 This highly depends on the Linux distribution. You can use the `CMAKE_INSTALL_PREFIX`
 variable to alter the default installation path.
-E.g: 
+E.g:
 
 `cmake -DCMAKE_INSTALL_PREFIX=/usr ..`
 
 Also, by default the build system enables a set of blocks used for debugging
-during the development. The enable/disable switch is controled through the 
+during the development. The enable/disable switch is controled through the
 `INCLUDE_DEBUG_BLOCKS` boolean variable. If for example, you want to disable the
 debugging blocks, the **CMake** command would be:
 
@@ -64,4 +65,4 @@ For more indormation about SatNOGS please visit our [site](https://satnogs.org/)
 
 © 2016,2017 [Libre Space Foundation](http://librespacefoundation.org).
 
-Licensed under the [GPLv3](LICENSE).
\ No newline at end of file
+Licensed under the [GPLv3](LICENSE).
diff --git a/lib/noaa_apt_sink_impl.cc b/lib/noaa_apt_sink_impl.cc
index e405736..efd61e6 100644
--- a/lib/noaa_apt_sink_impl.cc
+++ b/lib/noaa_apt_sink_impl.cc
@@ -31,6 +31,8 @@ namespace gr
 {
   namespace satnogs
   {
+    // Noaa apt sync pattern A
+    // (see https://sourceforge.isae.fr/attachments/download/1813/apt_synch.gif)
     const bool SYNCA_SEQ[] = {false, false, false, false,
                               true, true, false, false,   // Pulse 1
                               true, true, false, false,   // Pulse 2
@@ -42,6 +44,8 @@ namespace gr
                               false, false, false, false,
                               false, false, false, false};
 
+    // Noaa apt sync pattern B
+    // (see https://sourceforge.isae.fr/attachments/download/1813/apt_synch.gif)
     const bool SYNCB_SEQ[] = {false, false, false, false,
                               true, true, true, false, false,
                               true, true, true, false, false,
@@ -63,6 +67,7 @@ namespace gr
                                   flip));
     }
 
+
     /*
      * The private constructor
      */
@@ -90,6 +95,7 @@ namespace gr
       init_images();
     }
 
+
     void
     noaa_apt_sink_impl::init_images () {
         size_t len = d_filename_png.size();
@@ -109,6 +115,7 @@ namespace gr
         }
     }
 
+
     void
     noaa_apt_sink_impl::write_image (png::image<png::gray_pixel> image, std::string filename) {
         if(d_flip) {
@@ -130,6 +137,7 @@ namespace gr
         }
     }
 
+
     void
     noaa_apt_sink_impl::write_images () {
         write_image(d_full_image, d_full_filename);
@@ -140,6 +148,7 @@ namespace gr
         }
     }
 
+
     noaa_apt_sink_impl::~noaa_apt_sink_impl () {
         write_images();
     }
@@ -159,6 +168,7 @@ namespace gr
         }
     }
 
+
     void
     noaa_apt_sink_impl::skip_to (size_t new_x, size_t pos, const float *samples) {
         if(new_x > d_current_x) {
@@ -170,6 +180,7 @@ namespace gr
         d_current_x = new_x;
     }
 
+
     noaa_apt_sync_marker
     noaa_apt_sink_impl::is_marker(size_t pos, const float *samples) {
         size_t count_a = 0;
@@ -199,6 +210,7 @@ namespace gr
         }
     }
 
+
     int
     noaa_apt_sink_impl::work (int noutput_items,
                               gr_vector_const_void_star &input_items,
@@ -217,7 +229,6 @@ namespace gr
             if(d_synchronize_opt) {
                 if(is_marker(i, in) == noaa_apt_sync_marker::SYNC_A) {
                     skip_to(39, i, in);
-
                 }
                 else if(is_marker(i, in) == noaa_apt_sync_marker::SYNC_B) {
                     skip_to(d_width / 2 + 39, i, in);
diff --git a/lib/noaa_apt_sink_impl.h b/lib/noaa_apt_sink_impl.h
index 448add2..60357a5 100644
--- a/lib/noaa_apt_sink_impl.h
+++ b/lib/noaa_apt_sink_impl.h
@@ -71,21 +71,33 @@ namespace gr
             gr_vector_void_star &output_items);
 
     private:
+        // Generate empty images and filenames to save them to
         void
         init_images ();
 
+        /*
+         * Check if the history portion of the input contains a sync marker.
+         * Matches the 40 samples before pos against the patterns.
+         */
         noaa_apt_sync_marker
         is_marker (size_t pos, const float *samples);
 
+        // Set the pixel indicated by coordinates in the images (both full and split)
         void
         set_pixel (size_t x, size_t y, float sample);
 
+        /*
+         * Updates d_current_x to new_x,
+         * while using historical samples to fill any resulting gaps in the images.
+         */
         void
         skip_to (size_t new_x, size_t pos, const float *samples);
 
+        // Write the images to disk
         void
         write_images ();
 
+        // Write a single image to disk, also takes care of flipping
         void
         write_image (png::image<png::gray_pixel> image, std::string filename);
     };