On Wednesday, 12 August 2015 16:42:47 UTC+1, Desperate Dan wrote:
If my memory serves me correctly, CBRs in the early 70s only recorded up to 4000ft.

Yes you are correct.

The cloud base recorder was typical Met Office - designed by someone with an elecronics background and neither an observer or a forecaster. The chart was no more than 3x3" window in a large box (18x12" approx) of valves and circuits, it even had some kind of meter that was as big as the chart that recorded the cloud base!

Around the same time there was a visiometer that output to a Kent chart recorder which is probably what the CBR should have employed and would have been a lot more useful. I bet that came from outside the Office.

It's sad but I can still remember how it sounded as the arm moved up the chart...

Wasn't there a paper on the dispersal of night time cirrus at daybreak?