Radar altimeter help!

Is there a way to fix it? On various planes I will sometimes touch down when it reads 18 or I just might touch down at -38. Any way to fix this? Thank you in advance!
Flight Simulator and other chat
https://forums.simviation.com/phpBB3/
https://forums.simviation.com/phpBB3/viewtopic.php?f=20&t=56286