docs: Update for latest changs to skew_correction

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

1 files changed, 61 insertions, 20 deletions

diff --git a/docs/skew_correction.md b/docs/skew_correction.md
index f6b7822e..a787c9ed 100644
--- a/docs/skew_correction.md
+++ b/docs/skew_correction.md
@@ -1,6 +1,6 @@
 Software based skew correction can help resolve dimensional inaccuracies
 resulting from a printer assembly that is not perfectly square.  Note
-that if your printer is significantly skewed it is strongy recommended to
+that if your printer is significantly skewed it is strongly recommended to
 first use mechanical means to get your printer as square as possible prior
 to applying software based correction.
 
@@ -12,8 +12,9 @@ along the plane you want to correct.  There is also a
 that includes all planes in one model.  You want the object oriented
 so that corner A is toward the origin of the plane.
 
-Make sure that the [skew_correction] module is not enabled in printer.cfg
-prior to printing the calibration part.
+Make sure that no skew correction is applied during this print.  You may
+do this by either removing the [skew_correction] module from printer.cfg
+or by issuing a `SET_SKEW CLEAR=1` gcode.
 
 # Take your measurements
 The [skew_correcton] module requires 3 measurements for each plane you want
@@ -23,18 +24,56 @@ AD do not include the flats on the corners that some test objects provide.
 
 ![skew_lengths](img/skew_lengths.png)
 
-# Update printer.cfg
-Enter your lengths for the calibration print corresponding to the correct
-plane under the [skew_correction] section in printer.cfg, for example:
+# Configure your skew
+Make sure [skew_correction] is in printer.cfg.  You may now use the `SET_SKEW`
+gcode to configure skew_correcton.  For example, if your measured lengths
+along XY are as follows:
 ```
-[skew_correction]
-xy_ac_length: 140.4
-xy_bd_length: 142.8
-xy_ad_length: 99.8
+Length AC = 140.4
+Length BD = 142.8
+Length AD = 99.8
 ```
-Restart your printer.  If desired, you can reprint the calibration part
-with skew correction enabled. The following gcode can be used to calculate
-skew of a single plane and output the results:
+
+`SET_SKEW` can be used to configure skew correction for the XY plane.
+
+```
+SET_SKEW XY=140.4,142.8,99.8
+```
+You may also add measurements for XZ and YZ to the gcode:
+
+```
+SET_SKEW XY=140.4,142.8,99.8 XZ=141.6,141.4,99.8 YZ=142.4,140.5,99.5
+```
+
+The [skew_correction] module also supports profile management in a manner
+similar to [bed_mesh].  After setting skew using the `SET_SKEW` gcode,
+you may use the `SKEW_PROFILE` gcode to save it:
+
+```
+SKEW_PROFILE SAVE=my_skew_profile
+```
+After this command you will be prompted to issue a `SAVE_CONFIG` gcode to
+save the profile to persistent storage.  If no profile is named
+`my_skew_profile` then a new profile will be created.  If the named profile
+exists it will be overwritten.
+
+Once you have a saved profile, you may load it:
+```
+SKEW_PROFILE LOAD=my_skew_profile
+```
+
+It is also possible to remove an old or out of date profile:
+```
+SKEW_PROFILE REMOVE=my_skew_profile
+```
+After removing a profile you will be prompted to issue a `SAVE_CONFIG` to
+make this change persist.
+
+# Verifying your correction
+After skew_correction has been configured you may reprint the calibration
+part with correction enabled.  Use the following gcode to check your
+skew on each plane.  The results should be lower than those reported via
+`GET_CURRENT_SKEW`.
 
 ```
 CALC_MEASURED_SKEW AC=<ac_length> BD=<bd_length> AD=<ad_length>
@@ -42,11 +81,13 @@ CALC_MEASURED_SKEW AC=<ac_length> BD=<bd_length> AD=<ad_length>
 
 # Caveats
 
-When using the [skew_correction] module it is suggested to home all axes
-before attempting a move.  Homing a single axis to move could result in a
-correction along the x and/or y axis, potentially leading to a homing error.
+Due to the nature of skew correction it is recommended to configure skew
+in your start gcode, after homing and any kind of movement that travels
+near the edge of the print area such as a purge or nozzle wipe.   You may
+use use the `SET_SKEW` or `SKEW_PROFILE` gcodes to accomplish this.  It is
+also recommended to issue a `SET_SKEW CLEAR=1` in your end gcode.
 
-It is also important to keep in mind that it is possible for [skew_correction]
-to generate a correction that moves the tool beyond the printer's boundries
-on the X and/or Y axes.  It is recommended to arrange parts away from the
-edges when using [skew_correction].
+Keep in mind that it is possible for [skew_correction] to generate a correction
+that moves the tool beyond the printer's boundries on the X and/or Y axes.  It
+is recommended to arrange parts away from the edges when using
+[skew_correction].