Thank you, ZenTuner! 

I've been struggling with finding a tuner that reliably picks up the subcontrabass register, and I finally found one that seems to work down to C0 without much trouble: ZenTuner. Not only that, but it's free and open-source! And because the source code is available on the project's GitHub page (github.com/jps..., I was even able to modify my personal version to (somewhat) work even lower. There are still some tweaks I'd like to make to the display (labeled 5¢ increments rather than unlabeled 4¢ increments), and the function (I think if I could get it to use a larger sample size and update less regularly, it would be less noisy in the lowest range), but I'm extraordinarily relieved to find something that broadly works and that allows me to so easily make changes to better suit my admittedly niche needs! Huge thanks to the whole ZenTuner team!