I’ve just put some improved scans of the parts and schematics pages in the article – my original attempts were not very good!

And I’ve added a reference to the grey dialed Challenge Timer (‘bullhead’) – with many thanks to Jaliya (JAY48) who has helped research this model.  I’m now pretty sure that this was originally produced as an alternative to the black dialed version, the one with a printed Citizen logo. Hopefully I’ll be able to add a decent image of this one soon – edit> now added a pic with thanks again to Jaliya.