@wjdtn2909 ah I just noticed that you are using a TF-mini or other similar rangefinders.
in 4.0.7 and below we have a small bug that I have also mentioned here:
Sensors like the Lightware Sf40/c should work fine.
This has been fixed in Copter 4.1! its just the BendyRuler problem still exists though which will also be fixed soon. Sorry for the inconvenience. In 4.1 stable hopefully, everything will work out for you.
If you are keen on using BendyRuler till then, you can build this branch (if possible): GitHub - ArduPilot/ardupilot at Copter-4.0
The last change that has been pushed in this branch includes the fix you need for the Benwake rangefinders.