diff --git a/ArduCopter/Parameters.cpp b/ArduCopter/Parameters.cpp
index 162492ffd8..35ede3b051 100644
--- a/ArduCopter/Parameters.cpp
+++ b/ArduCopter/Parameters.cpp
@@ -1232,6 +1232,7 @@ const AP_Param::GroupInfo ParametersG2::var_info2[] = {
     // @DisplayName: EKF Failsafe filter cutoff
     // @Description: EKF Failsafe filter cutoff frequency. EKF variances are filtered using this value to avoid spurious failsafes from transient high variances. A higher value means the failsafe is more likely to trigger.
     // @Range: 0 10
+    // @Units: Hz
     // @User: Advanced
     AP_GROUPINFO("FS_EKF_FILT", 8, ParametersG2, fs_ekf_filt_hz, FS_EKF_FILT_DEFAULT),
 
diff --git a/ArduCopter/ekf_check.cpp b/ArduCopter/ekf_check.cpp
index 47d9121be9..c05e7a279c 100644
--- a/ArduCopter/ekf_check.cpp
+++ b/ArduCopter/ekf_check.cpp
@@ -123,7 +123,7 @@ bool Copter::ekf_over_threshold()
     }
 
     uint32_t now_us = AP_HAL::micros();
-    float dt = (now_us - last_ekf_check_us) / 1000000.0f;
+    float dt = (now_us - last_ekf_check_us) * 1e-6f;
 
     // always update filtered values as this serves the vibration check as well
     position_var = pos_variance_filt.apply(position_var, dt);