The Whiz Wheel in the military is the Dalton Computer.
The picture is of a computer that is a similar size to a Dalton Mk 4a. The Mk 5 is a mini-version intended for fast-jey cockpits etc. By the time I got a Mk 5 it was too small for me to see
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If you can get onto a flying unit you may be able to blag one out of stores. It is made by the London Name Plate Mfg. Co. Ltd. of London and Brighton and was marked "Computer Dead Reckoning Mk. 4A Ref. No. 6B/2645.
Or you might find a friendly Observer who can get you one, I think they are still C-stores.
Or look here:
http://cgi.ebay.co.uk/ARMY-AIR-FORCE...QQcmdZViewItem
The white one is the mk 4.
This is the same as the UK Mil Mk 4, ie without the compressibility features of the Mk 4a, but perfectly adequate for helicopters.
PS
Thank you for sharing that with us Samuraimatt, glad to see you have recovered.