diff --git a/G-Code-in-Marlin.md b/G-Code-in-Marlin.md
index 1aabfc6..16fb3fe 100644
--- a/G-Code-in-Marlin.md
+++ b/G-Code-in-Marlin.md
@@ -110,16 +110,17 @@ of M200 setting
 extrude-only move will be classified as retract depending on the direction  
 
 ###Z Probe
- [[G28]]  - Home one or more axes.  
- [[G29]]  - Probe the bed Z height at multiple points and enable bed leveling compensation.  
+ [[G28]]  - Home one or more axes. Note: G28 clears the bed leveling compensation matrix. Use G28 followed by G29 
+ [[G29]]  - Probe the bed Z height at multiple points and enable bed leveling compensation (ABL).  
  [[G30]]  - Probe the bed Z height at the current XY position.  
  [[G31]]  - Dock Z Probe sled.  
  [[G32]]  - Undock Z Probe sled.  
- [[M48]]  - Measure Z Probe repeatability.  
- [[M401]] - Lower Z-probe.  
- [[M402]] - Raise Z-probe.  
+ [[M48]]  - Measure Z Probe repeatability. To test the accuracy of your z probe (i.e. servo/switch Allen key or inductive probe). Returns the standard deviation in microns. 
+ [[M401]] - Lower Z-probe. Note: ABL with a servo. With an Allen key z-probe switch, ensure you are safe above the bed to clear the Allen key. 
+ [[M402]] - Raise Z-probe. Note: drives the servo 
  [[M420]] - Enable or disable Mesh Bed Leveling.  
  [[M421]] - Set a single Mesh Bed Leveling Z coordinate: X<pos> Y<pos> Z<pos>  
+ [[M851]] - Set/fine tune the z probe offset. M851 Z-6.90, store with M500 in EEPROM (if enabled).
 
 ###Filament Diameter
  [[M404]] - Set (or display) Nominal Filament Diameter in mm: [N<diameter>] (e.g., 3mm or 1.75mm)