Right, that’s the 12-litre cylinders delivered to Dive 90 in Cheltenham: the new one should sail past a visual inspection but the older one is up for a hydrostatic test and its ‘twin’ (purchased at the same time in 1999) failed a hydro two years ago.
For more information on diving cylinders, download this very comprehensive PDF file. (This was not written by me: if I knew who wrote it, I would acknowledge authorship.)