It is itself made of glass - the earliest form of projection known - and it's labelled up ready for use at Kerridge Odeon cinemas. If you can remember back that far you'll know that cinemas often showed single-shot adverts like this, especially for local products and events, usually with a local radio announcer's voiceover.

And here it is in closeup where you'll notice that standards of spelling - or maybe proof-reading - were no better in 1979 than they are now.