diff --git a/phc2sys.8 b/phc2sys.8
index 22f6f44..39a121c 100644
--- a/phc2sys.8
+++ b/phc2sys.8
@@ -101,13 +101,14 @@ the controller corrects by changing the clock frequency instead of stepping the
 clock. The clock is stepped on start regardless of the option if the offset is
 larger than 100 nanoseconds (unless the
 .BI \-F
-option is used). The value of 0.0 disables stepping after the start. The default
-is 0.0.
+option is used). It's specified in seconds. The value of 0.0 disables stepping
+after the start. The default is 0.0.
 .TP
 .BI \-F " step"
 Specify the step threshold applied only on the first update. It is the maximum
-offset that is corrected by adjusting clock. The value of 0.0 disables stepping
-on start. The default is 0.0000001 (100 nanoseconds).
+offset that is corrected by adjusting clock. It's specified in seconds. The
+value of 0.0 disables stepping on start.
+The default is 0.0000001 (100 nanoseconds).
 .TP
 .BI \-R " update-rate"
 Specify the slave clock update rate when running in the direct synchronization
diff --git a/ptp4l.8 b/ptp4l.8
index 5cf642f..dd5e33b 100644
--- a/ptp4l.8
+++ b/ptp4l.8
@@ -341,13 +341,14 @@ The default is 0.3.
 .B pi_offset_const
 The maximum offset the PI controller will correct by changing the clock
 frequency instead of stepping the clock. When set to 0.0, the controller will
-never step the clock except on start.
+never step the clock except on start. It's specified in seconds.
 The default is 0.0.
 .TP
 .B pi_f_offset_const
 The maximum offset the PI controller will correct by changing the clock
 frequency instead of stepping the clock. This is only applied on the first
-update. When set to 0.0, the controller won't step the clock on start.
+update. It's specified in seconds. When set to 0.0, the controller won't step
+the clock on start.
 The default is 0.0000001 (100 nanoseconds).
 .TP
 .B pi_max_frequency