Improve LIN_ADVANCE commentary (all configs)

Marlin/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled.
+ *
-// To get a rough start value for calibration, measure your "free filament length" between the hobbed bolt and the nozzle in cm.
+ * Assumption: advance = k * (delta velocity)
-// Then use the formula that fits your system, where L is the "free filament length":
+ * K=0 means advance disabled.
-// Filament diameter           |   1,75mm  |    3mm     |
+ * To get a rough start value for calibration, measure your "free filament length"
-// Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
-// Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/Cartesio/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/Felix/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/Hephestos/Configuration_adv.h

   #define D_FILAMENT 1.75
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/Hephestos_2/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/K8200/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/K8400/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/RigidBot/Configuration_adv.h

   #define D_FILAMENT 1.75
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/SCARA/Configuration_adv.h

   #define D_FILAMENT 1.75
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/TAZ4/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/WITBOX/Configuration_adv.h

   #define D_FILAMENT 1.75
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

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

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/delta/generic/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/delta/kossel_mini/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/delta/kossel_pro/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/delta/kossel_xl/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/makibox/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)

Marlin/example_configurations/tvrrug/Round2/Configuration_adv.h

   #define D_FILAMENT 2.85
 #endif
 
-// Implementation of a linear pressure control
+/**
-// Assumption: advance = k * (delta velocity)
+ * Implementation of linear pressure control
-// K=0 means advance disabled. A good value for a gregs wade extruder will be around K=75
+ *
+ * Assumption: advance = k * (delta velocity)
+ * K=0 means advance disabled.
+ * To get a rough start value for calibration, measure your "free filament length"
+ * between the hobbed bolt and the nozzle (in cm). Use the formula below that fits
+ * your setup, where L is the "free filament length":
+ *
+ * Filament diameter           |   1.75mm  |    3.0mm   |
+ * ----------------------------|-----------|------------|
+ * Stiff filament (PLA)        | K=47*L/10 | K=139*L/10 |
+ * Softer filament (ABS, nGen) | K=88*L/10 | K=260*L/10 |
+ */
 //#define LIN_ADVANCE
 
 #if ENABLED(LIN_ADVANCE)