Improve the Jerk description

Marlin/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/Cartesio/Configuration.h

 #define DEFAULT_MAX_FEEDRATE          {200,200,20,20}   // (mm/sec)
 #define DEFAULT_MAX_ACCELERATION      {1000,1000,100,10000}     // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for Skeinforge 40+, for older versions raise them a lot.
 
-#define DEFAULT_ACCELERATION          500    // X, Y, Z and E acceleration in mm/s^2 for printing moves
-#define DEFAULT_RETRACT_ACCELERATION  10000    // E acceleration in mm/s^2 for retracts
+#define DEFAULT_ACCELERATION          500     // X, Y, Z and E acceleration in mm/s^2 for printing moves
+#define DEFAULT_RETRACT_ACCELERATION  10000   // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   1000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                10.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/Felix/Configuration.h

 #define DEFAULT_MAX_FEEDRATE          {500, 500, 5, 25}    // (mm/sec)
 #define DEFAULT_MAX_ACCELERATION      {5000,5000,100,80000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for Skeinforge 40+, for older versions raise them a lot.
 
-#define DEFAULT_ACCELERATION          1750 //1500    // X, Y, Z and E max acceleration in mm/s^2 for printing moves
-#define DEFAULT_RETRACT_ACCELERATION  5000 // E acceleration in mm/s^2 for retracts
-#define DEFAULT_TRAVEL_ACCELERATION   3000 // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
-
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
-#define DEFAULT_XYJERK                10   // (mm/sec)
-#define DEFAULT_ZJERK                 0.3  //0.4   // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ACCELERATION          1750    // X, Y, Z and E max acceleration in mm/s^2 for printing moves
+#define DEFAULT_RETRACT_ACCELERATION  5000    // E acceleration in mm/s^2 for retracts
+#define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
+
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
+#define DEFAULT_XYJERK                10.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.3    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/Felix/DUAL/Configuration.h

 #define DEFAULT_MAX_FEEDRATE          {500, 500, 5, 25}    // (mm/sec)
 #define DEFAULT_MAX_ACCELERATION      {5000,5000,100,80000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for Skeinforge 40+, for older versions raise them a lot.
 
-#define DEFAULT_ACCELERATION          1750 //1500    // X, Y, Z and E max acceleration in mm/s^2 for printing moves
-#define DEFAULT_RETRACT_ACCELERATION  5000 // E acceleration in mm/s^2 for retracts
-#define DEFAULT_TRAVEL_ACCELERATION   3000 // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
-
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
-#define DEFAULT_XYJERK                10   // (mm/sec)
-#define DEFAULT_ZJERK                 0.3  //0.4   // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ACCELERATION          1750    // X, Y, Z and E max acceleration in mm/s^2 for printing moves
+#define DEFAULT_RETRACT_ACCELERATION  5000    // E acceleration in mm/s^2 for retracts
+#define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
+
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
+#define DEFAULT_XYJERK                10.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.3    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/Hephestos/Configuration.h

 #define DEFAULT_MAX_FEEDRATE          {200, 200, 3.3, 25}    // (mm/sec)
 #define DEFAULT_MAX_ACCELERATION      {1100,1100,100,10000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for Skeinforge 40+, for older versions raise them a lot.
 
-#define DEFAULT_ACCELERATION          650    // X, Y, Z and E acceleration in mm/s^2 for printing moves
-#define DEFAULT_RETRACT_ACCELERATION  1000   // E acceleration in mm/s^2 for retracts
+#define DEFAULT_ACCELERATION          650     // X, Y, Z and E acceleration in mm/s^2 for printing moves
+#define DEFAULT_RETRACT_ACCELERATION  1000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   1000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                10.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/Hephestos_2/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   1000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
 #define DEFAULT_ZJERK                  0.4    // (mm/sec)
 #define DEFAULT_EJERK                  2.0    // (mm/sec)

Marlin/example_configurations/K8200/Configuration.h

 #define DEFAULT_MAX_ACCELERATION      {9000,9000,100,10000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for Skeinforge 40+, for older versions raise them a lot.
 
 #define DEFAULT_ACCELERATION          1000    // X, Y, Z and E acceleration in mm/s^2 for printing moves
-#define DEFAULT_RETRACT_ACCELERATION  1000   // E acceleration in mm/s^2 for retracts
+#define DEFAULT_RETRACT_ACCELERATION  1000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   1000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/K8400/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  6000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                10.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.5     // (mm/sec)
+#define DEFAULT_ZJERK                  0.5    // (mm/sec)
 #define DEFAULT_EJERK                 20.0    // (mm/sec)
 
 

Marlin/example_configurations/K8400/Dual-head/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  6000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                10.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.5     // (mm/sec)
+#define DEFAULT_ZJERK                  0.5    // (mm/sec)
 #define DEFAULT_EJERK                 20.0    // (mm/sec)
 
 

Marlin/example_configurations/RepRapWorld/Megatronics/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/RigidBot/Configuration.h

 // @section motion
 
 #define DEFAULT_AXIS_STEPS_PER_UNIT   {44.3090, 22.1545, 1600, 53.5}  // default steps per unit for RigidBot with standard hardware
-                                                                      // default steps for 16-teth polleys {100.06,50.06,1600,76},  HPX2-MAX E=504, RigidBot E=53.5, Peter Stoneham's=76
+                                                                      // default steps for 16-tooth pulleys {100.06,50.06,1600,76},  HPX2-MAX E=504, RigidBot E=53.5, Peter Stoneham's=76
 #define DEFAULT_MAX_FEEDRATE          {500, 500, 5, 25}    // (mm/sec)
 #define DEFAULT_MAX_ACCELERATION      {800, 800, 100, 10000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for Skeinforge 40+, for older versions raise them a lot.
 
-#define DEFAULT_ACCELERATION          600    // X, Y, Z and E acceleration in mm/s^2 for printing moves
-#define DEFAULT_RETRACT_ACCELERATION  1000   // E acceleration in mm/s^2 for retracts
-#define DEFAULT_TRAVEL_ACCELERATION   3000   // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
+#define DEFAULT_ACCELERATION          600     // X, Y, Z and E acceleration in mm/s^2 for printing moves
+#define DEFAULT_RETRACT_ACCELERATION  1000    // E acceleration in mm/s^2 for retracts
+#define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
-#define DEFAULT_XYJERK                8.0    // (mm/sec)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
+#define DEFAULT_XYJERK                8.0     // (mm/sec)
 #define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_EJERK                 5.0     // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/SCARA/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  2000   // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   400    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
-#define DEFAULT_XYJERK                5    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4    // (mm/sec)
-#define DEFAULT_EJERK                 3    // (mm/sec)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
+#define DEFAULT_XYJERK                5.0     // (mm/sec)
+#define DEFAULT_ZJERK                 0.4     // (mm/sec)
+#define DEFAULT_EJERK                 3.0     // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/TAZ4/Configuration.h

 #define DEFAULT_MAX_FEEDRATE          {800, 800, 8, 50}    // (mm/sec)
 #define DEFAULT_MAX_ACCELERATION      {9000,9000,100,10000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for Skeinforge 40+, for older versions raise them a lot.
 
-#define DEFAULT_ACCELERATION          500    // X, Y, Z and E acceleration in mm/s^2 for printing moves
+#define DEFAULT_ACCELERATION          500     // X, Y, Z and E acceleration in mm/s^2 for printing moves
 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
-#define DEFAULT_XYJERK                8.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
+#define DEFAULT_XYJERK                 8.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
 #define DEFAULT_EJERK                 10.0    // (mm/sec)
 
 

Marlin/example_configurations/WITBOX/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                10.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/adafruit/ST7565/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/delta/biv2.5/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                15.0    // (mm/sec)
 #define DEFAULT_ZJERK                 15.0    // (mm/sec) Must be same as XY for delta
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/delta/generic/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
 #define DEFAULT_ZJERK                 20.0    // (mm/sec) Must be same as XY for delta
-#define DEFAULT_EJERK                 5.0     // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/delta/kossel_mini/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
 #define DEFAULT_ZJERK                 20.0    // (mm/sec) Must be same as XY for delta
-#define DEFAULT_EJERK                 5.0     // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/delta/kossel_pro/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
 #define DEFAULT_ZJERK                 20.0    // (mm/sec) Must be same as XY for delta
-#define DEFAULT_EJERK                 5.0     // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/delta/kossel_xl/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
 #define DEFAULT_ZJERK                 20.0    // (mm/sec)
 #define DEFAULT_EJERK                 20.0    // (mm/sec)

Marlin/example_configurations/makibox/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   3000    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================

Marlin/example_configurations/tvrrug/Round2/Configuration.h

 #define DEFAULT_RETRACT_ACCELERATION  3000   // E acceleration in mm/s^2 for retracts
 #define DEFAULT_TRAVEL_ACCELERATION   500    // X, Y, Z acceleration in mm/s^2 for travel (non printing) moves
 
-// The speed change that does not require acceleration (i.e. the software might assume it can be done instantaneously)
+// "Jerk" specifies the minumum speed change that requires acceleration.
+// When changing speed and direction, if the difference is less than the
+// value set here, it may happen instantaneously.
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
-#define DEFAULT_ZJERK                 0.4     // (mm/sec)
-#define DEFAULT_EJERK                 5.0    // (mm/sec)
+#define DEFAULT_ZJERK                  0.4    // (mm/sec)
+#define DEFAULT_EJERK                  5.0    // (mm/sec)
 
 
 //===========================================================================