![](http://farm3.static.flickr.com/2625/3879405834_1bbaa42743.jpg)
The bits, usb numeric keypad (but any keyboard would do the job), reed switch, phone plug and socket, solder etc.
![](http://farm3.static.flickr.com/2492/3878610199_1a53c4e8e3.jpg)
Open it up and fit the phone socket.
![](http://farm3.static.flickr.com/2492/3878610199_1a53c4e8e3.jpg)
Connect two wires from the socket across one of the key positions, avoid system keys such as backspace and enter.
![](http://farm3.static.flickr.com/2559/3878609949_1b5c03c014.jpg)
Close it all up again.
![](http://farm4.static.flickr.com/3479/3879405262_f8f0ae6eda.jpg)
Connect the reed switch and the phone plug to a length of flex.
![](http://farm4.static.flickr.com/3470/3878609737_7373fba372.jpg)
All the bit together.
![](http://farm3.static.flickr.com/2629/3879405048_8f416fbc36.jpg)
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)
![](http://farm3.static.flickr.com/2466/3879404926_89423f9b6d.jpg)
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!