In servicing this Zuckermann,

Jacks awaiting regulation

fitting new quills…

The Apron Workbench

I remembered – just in time – that it’s essential to check the strings’ seating on the bridge:

Strings can ride up the pins

because the strings can easily ride up the  bridge pins – and remain ‘hanging’ there. By the way, this is also just as true of pianos (though the movement is much smaller) – so tapping the strings into the bridge pin angle stabilises not only the tone and tuning, but also the regulation.