Precision Altimeters
 

https://cimg0.ibsrv.net/gimg/pprune....f0e928ded7.jpg
Personally I would have called these high altitude barometers as they only read pressure from 100-300mb.
They were reportedly fitted to a Valiant, possibly XD818, but what would they have been used for?
I was asked this question on Facebook after posting images of Varsity instruments and radio boxes.
I have never seen them before.

Google search of images for [precision altimeter] returns a couple of quite similar hits. One very similar.
https://www.worthpoint.com/worthoped...ter-1778306776
Negretti Zambra precision altimeter

I guess it might say "Negretti & Zambra" under those Stbd and Port labels.

Here is a facebook page by an ex-employee.

https://www.facebook.com/people/Negr...0057295096589/
"the great firm I joined in 1979 aged 16. NZ is now part of Meggitt"

There are images of your "Port" device.
https://cimg2.ibsrv.net/gimg/pprune....09af1b5b14.png



https://cimg9.ibsrv.net/gimg/pprune....eb3aad215c.jpg

https://hydrography.pro/presta17/alt...altimeter.html
https://cimg1.ibsrv.net/gimg/pprune....bcb4092668.jpg

https://vavasseur-antiques.com/portf...mbra-p-157780/
https://cimg0.ibsrv.net/gimg/pprune....582e13b8e3.jpg