docs: Rename Documents

Signed-off-by: Yifei Ding <yifeiding@protonmail.com>

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+# Skew correction
+
+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 strongly recommended to
+first use mechanical means to get your printer as square as possible prior
+to applying software based correction.
+
+## Print a Calibration Object
+
+The first step in correcting skew is to print a
+[calibration object](https://www.thingiverse.com/thing:2563185/files)
+along the plane you want to correct.  There is also a
+[calibration object](https://www.thingiverse.com/thing:2972743)
+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 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
+to correct; the length from Corner A to Corner C, the length from Corner B
+to Corner D, and the length from Corner A to Corner D.  When measuring length
+AD do not include the flats on the corners that some test objects provide.
+
+![skew_lengths](img/skew_lengths.png)
+
+## 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:
+
+```
+Length AC = 140.4
+Length BD = 142.8
+Length AD = 99.8
+```
+
+`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>
+```
+
+## Caveats
+
+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.
+
+Keep in mind that it is possible for `[skew_correction]` to generate a correction
+that moves the tool beyond the printer's boundaries on the X and/or Y axes.  It
+is recommended to arrange parts away from the edges when using
+`[skew_correction]`.