Solved!   (see below)

"Harper Patent Overhead Height Checker"

I've come across a bit of kit the purpose of which I can only guess at.

My name is Chris Hammond, and I'm a pilot by trade. My Dad was a member of the ROC in Lincolnshire during the war before he was called up which made me think of them when I was shown a mysterious object today, a 'Harper Patent Overhead Height Checker'.

This thing is about the size and shape of a thick pencil, and has a plug at one end which comes out and has a red thread attached, obviously for measuring something. Written on the pencil are many types of aircraft names, both German and Allied, and a lot of dimensions. Wingspans at a guess. It struck me that this could have been used in conjunction with silhouettes to identify passing a/c.

I wonder if anybody ex-ROC may be able to supply any more information, if only for my own interest.

Chris Hammond

A member of  the Cornish Aviation Society has forwarded to Lawrence :-

"The Aeroplane Spotter of 29.6.43 gives the source of supply. Now fitted with patent sliding cursor, can still be obtained , with full working instructions, from F.Harper, Esq., "Southcliffe", Selby Road, Fulford, York. To date about 9,000 Height Checkers have been supplied and they cost 4s each post free."   Does the 'Patents Office' have records ?

Joe James, a WWII observer of 10 Group, replies :-

"What you describe was a device for estimating the height of aircraft. It was a pretty hit or miss way of estimating height. You held the device, the length of the piece of string, away from your eye. You then read off the reading on the device which gave you the height as long as you knew the wing span of the aircraft. As I said - a pretty hit or miss estimation. I have a feeling I had one of these - 60 years ago !!!!!"

Lawrence Holmes:-     I think the above clarifies that it was a privately produced device for obtaining the height of an aircraft and not official issue to the ROC. I have never seen nor heard of one before - so well done !

[13apr07 18:45]