Hi Harold,
I just realized that you are using the SignalHound 2.18D software. In that case there is no way to clear the limit line short of closing the software. I apologize for the inconvenience.
On the other hand, if you are interested, we have released a new software interface for our spectrum analyzers. It is called Spike, and can be downloaded for free here, http://www.productbundlesdemo.kinsta.cloud/Spike. It can be installed along side your existing application. Going forward, it is what we recommend to new users. Along with many other additions, you can clear the limit lines in the software.
Let me know if you have further questions.
Regards,
A.J.
