diff --git a/kernel/fstdata.h b/kernel/fstdata.h
index 7f763b621..43f779cb5 100644
--- a/kernel/fstdata.h
+++ b/kernel/fstdata.h
@@ -69,7 +69,7 @@ private:
 	uint64_t last_time;
 	std::map<fstHandle, std::string> past_data;
 	uint64_t past_time;
-	int scale;
+	int scale; // exponent of 10, e.g. -6 = us, -9 = ns
 	std::string timescale_str;
 	uint64_t start_time;
 	uint64_t end_time;
diff --git a/passes/sat/sim.cc b/passes/sat/sim.cc
index 23bb076f2..1be993154 100644
--- a/passes/sat/sim.cc
+++ b/passes/sat/sim.cc
@@ -55,7 +55,7 @@ static const std::map<std::string, int> g_units =
 
 struct scaled_time {
 	uint64_t time;
-	int scale;
+	int scale; // exponent of 10, e.g. -6 = us, -9 = ns
 	bool end;
 };