One of the features of the Mixbus product is a K-meter, based on the concept introduced by Bob Katz.
Out of curiosity, I did some googling to see if I could find a K-meter plugin to use with Ardour, and came up with this:
It operates as a standalone Jack-enabled application, or a VST plugin. It’s free (ie no cost and GPL 3). Haven’t used it, but thought it might be of interest to some users?
Just search for “k-meter bob katz” if you are not familiar with the concept.
Regards, Paul H