Ok as promised, here are the photos of the calculator, it is one of the few that provides direct access to some engineering terms, T,G,M,u,m,k,f,p & n etc. The holy grail of course would be the Casio fx-61 with its dedicated electrical functions, but they are serious money.
As is always the case with these dual power calculators, the internal battery was toast, reading just .6v instead of 3v, so a quick clean of the contacts and a new battery it was back up and running in no time. Now to try and locate a decent copy of the owners manual for it, I have found some, but they all suffer from terrible scan quality that make of the instructions difficult to make out.
Edit: Oh and yes it has that equals key
![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif)
![](https://i.imgur.com/cS6XqCNh.jpg)