The bits, usb numeric keypad (but any keyboard would do the job), reed switch, phone plug and socket, solder etc.
Open it up and fit the phone socket.
Connect two wires from the socket across one of the key positions, avoid system keys such as backspace and enter.
Close it all up again.
Connect the reed switch and the phone plug to a length of flex.
All the bit together.
Mount the reed switch close to the lead screw and stick a magnet on the leadscrew.
(Do not forget to clean your lathe before taking photographs)
A bit of software and there we have a nice big number to watch on the old laptop!
BTW, that not our tablecloth! It is an old rag on the bench in the 'shop!
