Hello Johnmac, thank you for supporting pianoscope! It's great that you find it useful for aural tuning.
The beat rate that is displayed in the top right corner of the partials view is calculated from the tuning target pitches which are derived from the inharmonicity of the instrument and the chosen tuning style. The beating from actual recorded notes can differ from the calculated beat rates if the recorded strings are at a different pitch. I don't currently show the actual beat rates of the partials. But I could implement this as a new feature in a future version.