Merge pull request #546 from wes-johnson/104

Added 'well known properties' with engUnit to the spec

Author: wes-johnson

.gitignore

@@ -14,3 +14,4 @@ Sparkplug_TCK_*.zip
 tck/Sparkplug_TCK_*.zip
 .pydevproject
 tck/webconsole/yarn.lock
+tck/webconsole/package-lock.json

specification/src/main/asciidoc/chapters/Sparkplug_6_Payloads.adoc

@@ -599,7 +599,6 @@ string to represent it.
 ** This is a freeform field with a UTF-8 string to represent any other pertinent metadata for this
 metric. It can contain JSON, XML, text, or anything else that can be understood by both the
 publisher and the subscriber.
-
 [[payloads_b_propertyset]]
 ==== PropertySet
 
@@ -658,6 +657,22 @@ can be found here: https://developers.google.com/protocol-buffers/docs/proto#sca
 *** Sparkplug _PropertySetList_
 **** Defined link:#payloads_b_propertysetlist[here].
 
+[[payloads_b_well_known_properties]]
+==== Well Known Properties
+
+[cols="1,5"]
+|===
+|*Key Name*
+|*Value*
+
+|engUnit
+|UNECE codes for 'units of measure' are recommended
+
+|readOnly
+|True or False
+|===
+
+
 [[payloads_b_quality_codes]]
 ===== Quality Codes