When did you last hear of an alidade being used (unless the name has been nicked to apply to the thingy you squint through on modern, electronic devices!)

You're quite right Rhuby, I don't think it is in use now, but like Faldage I certainly used one in the '60s and according to this 'ere dictionary "In USA the term is also applied to the telescope and its attachments on a theodolite...". So there we are then. Mind you, I did say the dictionary dated from 1958. Some of the stuff in it is downright quaint.