doc: mention dependency of net corrections on HW timestamping

diff --git a/doc/chrony.conf.adoc b/doc/chrony.conf.adoc
index abb8403c1dff52588ef8d9e13d1e66f68111af5f..cb3f95c0ff013aa00ea31615769078acc41d612c 100644 (file)
--- a/doc/chrony.conf.adoc
+++ b/doc/chrony.conf.adoc
@@ -339,8 +339,10 @@ Protocol (PTP) correction field in NTP-over-PTP messages updated by one-step
 end-to-end transparent clocks in network switches and routers to significantly
 improve accuracy and stability of the synchronisation. NTP-over-PTP can be
 enabled by the <<ptpport,*ptpport*>> directive and setting the *port* option to
-the PTP port. This field should be enabled only for servers known to be running
-*chronyd* version 4.5 or later.
+the PTP port. The corrections are applied only to NTP measurements with HW
+timestamps (enabled by the <<hwtimestamp,*hwtimestamp*>> directive). This
+field should be enabled only for servers known to be running *chronyd* version
+4.5 or later.
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