diff --git a/main.c b/main.c
index 030ae77..96d1929 100644
--- a/main.c
+++ b/main.c
@@ -33,13 +33,13 @@
 
 int main(void)
 {
-  sp_init(); // initialize the serial protocol
-  settings_init();
-  plan_init(); // initialize the stepper plan subsystem
-  st_init(); // initialize the stepper subsystem
-  spindle_init(); // initialize spindle controller
-  gc_init(); // initialize gcode-parser
-  
+  sp_init();        
+  settings_init();  
+  plan_init();      
+  st_init();        
+  spindle_init();   
+  gc_init();        
+                    
   for(;;){
     sleep_mode(); // Wait for it ...
     sp_process(); // ... process the serial protocol
diff --git a/motion_control.c b/motion_control.c
index 36c5bd8..f1f1b45 100644
--- a/motion_control.c
+++ b/motion_control.c
@@ -36,14 +36,6 @@ void mc_dwell(uint32_t milliseconds)
   _delay_ms(milliseconds);
 }
 
-// Execute linear motion in absolute millimeter coordinates. Feed rate given in millimeters/second
-// unless invert_feed_rate is true. Then the feed_rate means that the motion should be completed in
-// 1/feed_rate minutes.
-// void mc_line(double x, double y, double z, double feed_rate, int invert_feed_rate)
-// {
-//   plan_buffer_line(x, y, z, feed_rate, invert_feed_rate);
-// }
-
 // Execute an arc. theta == start angle, angular_travel == number of radians to go along the arc,
 // positive angular_travel means clockwise, negative means counterclockwise. Radius == the radius of the
 // circle in millimeters. axis_1 and axis_2 selects the circle plane in tool space. Stick the remaining
diff --git a/motion_control.h b/motion_control.h
index 11123b0..d2f409b 100644
--- a/motion_control.h
+++ b/motion_control.h
@@ -28,9 +28,8 @@
 // unless invert_feed_rate is true. Then the feed_rate means that the motion should be completed in
 // (1 minute)/feed_rate time.
 #define mc_line(x, y, z, feed_rate, invert_feed_rate) plan_buffer_line(x, y, z, feed_rate, invert_feed_rate) 
-// NOTE: Although this function structurally belongs in this module, there is nothing to to but
-// to forward the request to the planner. For efficiency the function is replaced with a macro that
-// just forwards the call to the planner.
+// NOTE: Although this function structurally belongs in this module, there is nothing to do but
+// to forward the request to the planner. For efficiency the function is implemented with a macro.
 
 // Execute an arc. theta == start angle, angular_travel == number of radians to go along the arc,
 // positive angular_travel means clockwise, negative means counterclockwise. Radius == the radius of the
diff --git a/planner.c b/planner.c
index 8102eec..90b93f2 100644
--- a/planner.c
+++ b/planner.c
@@ -66,12 +66,12 @@
 // The number of linear motions that can be in the plan at any give time
 #define BLOCK_BUFFER_SIZE 20  
 
-block_t block_buffer[BLOCK_BUFFER_SIZE];  // A ring buffer for motion instructions
-volatile int block_buffer_head;           // Index of the next block to be pushed
-volatile int block_buffer_tail;           // Index of the block to process now
+static block_t block_buffer[BLOCK_BUFFER_SIZE];  // A ring buffer for motion instructions
+static volatile int block_buffer_head;           // Index of the next block to be pushed
+static volatile int block_buffer_tail;           // Index of the block to process now
 
 // The current position of the tool in absolute steps
-int32_t position[3];   
+static int32_t position[3];   
 
 static uint8_t acceleration_manager_enabled;   // Acceleration management active?
 
diff --git a/planner.h b/planner.h
index b31ffb9..71524b9 100644
--- a/planner.h
+++ b/planner.h
@@ -51,8 +51,6 @@ typedef struct {
   
 } block_t;
       
-extern int32_t position[3];
-
 // Initialize the motion plan subsystem      
 void plan_init();
 
diff --git a/stepper.c b/stepper.c
index d0828eb..933b847 100644
--- a/stepper.c
+++ b/stepper.c
@@ -55,7 +55,7 @@ static int32_t counter_x,       // Counter variables for the bresenham line trac
                counter_y, 
                counter_z;       
 static uint32_t step_events_completed; // The number of step events executed in the current block
-volatile int busy; // TRUE when SIG_OUTPUT_COMPARE1A is being serviced. Used to avoid retriggering that handler.
+static volatile int busy; // TRUE when SIG_OUTPUT_COMPARE1A is being serviced. Used to avoid retriggering that handler.
 
 // Variables used by the trapezoid generation
 static uint32_t cycles_per_step_event;        // The number of machine cycles between each step event