Does anybody know exactly what this is please?

Discussion in 'Weapons, Equipment & Rations' started by trademarklondon, Nov 3, 2010.

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    Small brass instrument with half mirror, hanging ring and plumb bob that swings 180° around a strangely calibrated, semi-circular scale.
    Hanging ring external diameter 25mm.
    Black square frame attached point to point to create a "diamond", which is half-mirrored. This black frame can be rotated into four positions around the perpendicular axis of the instrument, each position 90° apart and held in place by a spring detent (see black spring assembly on shaft between the scale and the black frame).
    Brass semi-circular scale with irregular markings, where the distance between 5 and 10 is four times that between 10 and 15, and which distances get shorter as the values increase, except after 30 and 40 where the distances get progressively longer again.
    A pendulum swings around the fulcrum at the natural centre of the scale. This pivot has a knurled clamp nut that can be tightened to lock the pendulum in any position.
    The brass block on the pendulum can be slid along the pendulum shaft and has approximately 10mm of possible movement.
    The wording "1 in" are embossed on the pendulum shaft, which makes one think it could mean one in five, ten etc., according to where the "blade" of the pendulum intersects the scale. If this were so it cannot possibly read right, as one in 55 would be a very shallow angle, around 2%, and one in 5 would be an angle of about 20%, which isn't exactly steep..... but if you apply this, those two values would equate to about 30 degrees of arc, possibly slightly more.... but the arc on the scale extends over 180° for those values, and the values are not constant in their spacing.
    Overall length of the instrument from top of hanging ring to base of pendulum is 21cm, but it folds to fit into a smaller leather case.
    Half mirrors do not work on their own. They have to be combined with at least one other mirror in order to bring two targets together into one image, such as in a sextant, mirror clinometer, range finder, etc.... so my thought is this instrument cannot be used on its own, but must be used as an integral part of a larger instrument or weapon.
    All I really know is that this instrument is rare... there are very few in existence, and there were very few in the early 1950s when they were still in use.
    The instrument has no "sights" or optics, as would be expected of a clinometer.

    DOES ANYBODY RECOGNISE THIS INSTRUMENT? I can email, skype or msn more photos if necessary.
  2. Obviously for measuring the "angle of dangle" as any fule kno...!
  3. nah! not big enough :) In case I forgot to mention it has the military arrow - the instrument that is, not the dangle :)
  4. Brass = RN?

    Looks like a calibrator for the telescopic direct-fire sight on a naval gun.
  5. It's something to do with gunnery, but it has the army broad arrow, so fairly sure it's not RN or RAF - WW2 RAF items were marked AM and RN items didn't carry the arrow. Also the scale is weird... it's not in degrees, and the gradations are not constant. I know it is Army, and it dates to WW2 and that it is very rare... and that several were sent back to F. Barker & Son Ltd in the early 1950s, just after the war, for repair, but when the factory asked what they were used for that information was declined - they were just told to repair them. It must be part of a larger item - but what?
  6. Now that I can see the scale clearly, I've some idea of how it probably works. Rotate the black square through 90 degrees from where it is in your photo and extend the siding weight. Align the bottom of the mirror with, say, the skylined top of a slope. Read off the angle shown, given as 1 in xx, the pre-metric method of measuring road slopes.

    Why it needs to have a mirror as opposed to just a straight edge, I don't know, but it's ticking along in my imagination.


    As you've mentioned, the scale doesn't make sense. Is there anything else that moves?
  7. Quite sure - Abbey guessed - they didn't actually know - I've spoken to them. I have seen three of these in all my years of repairing instruments - all bore the military arrow, one bore the maker's name, Palmer, and one bore the date 1943.

    Also, a previous owner of Francis Barker Limited confirmed they were still in use by the army in the early 1950s, as he remembers repairing them, but also remembers not being told what they were, which made repairs a little challenging.

    So yes, absolutely certain of WW2 to early 1950s.
  8. Lancaster Archive Forum posted on my behalf, and the following blog also carries it, which is my own blog:

    Trade Mark London Blog!
  9. putteesinmyhands, tried that.... tried every possible method of use, and I have used and repaired just about every known clitometer over the years - I call them clitometers, more fun than measuring angle of dangle - and this one cannot be used on its own. All half-mirror instruments work with a second part that has at least one other mirror, such as a sextant.
  10. Cancel my last, it's simpler than I thought. Don't rotate the black square. The graduation plate operates in an approximately horizontal position so that small movements give large changes in measurements. The mirror must have some function in preventing the operator from tilting the device fore/aft.
  11. jim24

    jim24 Book Reviewer

  12. Hi putteesinmyhands - no that doesn't work either.

    I have been repairing and servicing military instruments for countless years and I can use, identify calibrate and repair any instrument - or so I thought - this one has stumped not just me, but also experts at the British War Museum.

    What I'm looking for is not guesswork - I've already been through all that - I am just looking for somebody who can positively say

    "I have used one of those, I know exactly what it is and what it is used for"

    This instrument CANNOT be used on its own, it has to be part of a larger complex - the single half mirror proves that - single half mirrors can ONLY be used with other single half mirrors, such as in a sextant, or a mirror clitometer.

    Guessing will not work in this case - I really need to find somebody who actually USED one of these - and was hoping maybe sometime somebody in these forums would see it and remember having actually used it.

    I appreciate all your enthusiasm, I know it's tempting to have a guess, and I'd probably do the same, but I'm really looking for a 100% identification.

    Thanks all :)