A section of arc measuring device maybe. Any other suggestions?

[Anorak Bob]

One of the architects I work with brought this in today for me to have a look at. I had the Nikon with me. I've never seen anything like it before. The weighted point stays in place and when the other pointed arm is moved the graduated roller rolls. Nifty.

It is 250mm in length.

Anyone by chance know what it is?

BT

[marty989]

It is a planimeter

Planimeters (http://www.mathsinstruments.me.uk/page38.html)

[Stustoys]

Hi BT
Is it an automatic area measuring machine?

Stuart

[Anorak Bob]

It is a planimeter

Planimeters (http://www.mathsinstruments.me.uk/page38.html)

You blokes are on the ball!:2tsup: I've wired the link off to the owner. He'll be chuffed.

BT

[Stustoys]

I never would have come up with the name for it though. Now if I could just get my head around how they work!

Stuart

[franco]

I never would have come up with the name for it though. Now if I could just get my head around how they work!

Stuart

Stuart,

Have a look here for some information on how they work, and some of the types of jobs they were used for in pre-computer days:

What is this tool? (http://www.practicalmachinist.com/vb/general-archive/what-tool-94094/)

You need a very steady hand to get consistent results!

B T: There is often a metal strip in the case wth a spike on one end and a notch in the other for a pencil lead which allows you to draw a circle of known area for calibration purposes - I don't see one in your photos. What is the round object in the end of the case? Does it look as if it might be used for this purpose? Otherwise they can be calibrated by drawing a square of known area.

Frank

[Stustoys]

Hi Frank,
Thanks for that I'll have a read.
I think you'll find the round object fitted in the last two pictures. I had it down as a weight to hold that end in place?

Stuart

[franco]

Hi Frank,
Thanks for that I'll have a read.
I think you'll find the round object fitted in the last two pictures. I had it down as a weight to hold that end in place?

Stuart

Stuart,

Thanks - I think you are probably right. From memory, on the ones I used the weight was integral with the arm. In my defence I can only say it's at least 45 years since I've used one - a circumstance I regret not at all! However, they are a very interesting (if frustrating) tool for measuring irregular areas, and other similar purposes detailed by various posters in the thread linked to in my previous post.

Frank.

[Anorak Bob]

Stuart,

Thanks - I think you are probably right. From memory, on the ones I used the weight was integral with the arm. In my defence I can only say it's at least 45 years since I've used one - a circumstance I regret not at all! However, they are a very interesting (if frustrating) tool for measuring irregular areas, and other similar purposes detailed by various posters in the thread linked to in my previous post.

Frank.

Sorry Frank,

I've been dragging my feet. It is a weight.

Bob.

[Stustoys]

Still struggling with how these things work.
I found this page which helps with the math.
The Planimeter (http://whistleralley.com/planimeter/planimeter.htm)
Though I struggle with the numbers not being back to zero when you return to the start point..:D.. but I think I'm getting it.

Stuart

[franco]

Still struggling with how these things work.
I found this page which helps with the math.
The Planimeter (http://whistleralley.com/planimeter/planimeter.htm)
Though I struggle with the numbers not being back to zero when you return to the start point..:D.. but I think I'm getting it.

Stuart

Stuart,

The pointer on the planimeter must, of course, come back to the exact starting point on the diagram after it is moved around the perimeter of the diagram. Otherwise the numbers on the planimeter will be meaningless, because it takes into account the distance travelled and the angle, positive and negative, relative to the start point each time the planimeter pointer is moved, so must come back to the start point to finish the calculation. If the numbers came back to zero (or the starting number - some older planimeters don't have a quick zero reset and it is quicker to keep going from the previous reading) you would have a zero area. You will get this if you run the planimeter "around" a single straight line where the sum of the two positive and two negative movements when you return to the starting point is zero because the line has no thickness.

It's like an automatic counter which stops after each batch of parts. You can either note the total and reset the counter to zero for the next batch, or note the new starting point and continue on.

Sometimes you can set the planimeter to give a direct reading in the units required, e.g. hectares, square feet, square millimetres, but often you will have to apply a correction factor to the raw numbers from the planimeter to get an answer in the required units.

Frank

[Ueee]

Hi,
Very interesting......like Stuart i think the name is a bit strange.....a planimeter. Anyone know what Plani is in English(from whatever language it is)? At a guess i would say area......Amazingly an ebay search comes up with a few. planimeter | eBay (http://www.ebay.com.au/sch/i.html?_from=R40&_trksid=p3984.m570.l1313&_nkw=planimeter&_sacat=See-All-Categories)

[SurfinNev]

I think I have the same one as this -

A.OTT PLANIMETER. | eBay (http://www.ebay.com.au/itm/A-OTT-PLANIMETER-/320950663558)

Don't know why I bought it but they are interesting little gadgets.

Nev

[Anorak Bob]

Nev,

Several years ago I saw a beautiful A. Ott pantograph in a pawn shop. They wanted a Mawson for the thing which I thought at the time was stiff. A beautiful bit of gear but I couldn't see a use for it.

A just had a quick Ebay skim and found this Ott offering -

ANCIEN APPAREIL DE MESURE D'ECOULEMENT D'EAU-A OTT-KEMPTEM | eBay (http://www.ebay.com.au/itm/ANCIEN-APPAREIL-MESURE-DECOULEMENT-DEAU-A-OTT-KEMPTEM-/251119057418?pt=FR_JG_Collections_Sciences&hash=item3a77dcba0a)

There's always something! :U

BT

[Stustoys]

Come on Bob you know you want one, though part of that one is broken(I think).
Anyone know how the diamond pattern is done?

Hi Frank,
Thanks, I've finally got it, I think the easiest way for me to get it was if I take this java to the extreme.

Rail Planimeter (http://whistleralley.com/java/railplan.htm)

With the green arm square to the black line move down the page, the wheel moves at same speed as the pointer. (make that one side)
Move the pointer to the black line, the wheel moves some unknowm amount(make that side two)
Move back up the black line, the wheel wont turn at all(side three)
Move back out to the start point, the wheel moves the same unknowm amount in reverse as side two(side four)
and you have a number.

Stuart

[joe greiner]

Many years ago, in his Mathematical Games section of Scientific American, Martin Gardner described a "hatchet planimeter," which was a simple hatchet with a tracing point at the far end of the handle. After tracing the perimeter of the measured area, the blade left a zig-zag trail. The transverse width of the trail was proportional to the area. To find the proportion factor, trace a known area, such as a 1-inch square. The wheel of the modern planimeter serves a similar function as the hatchet planimeter's blade.

Google [hatchet planimeter] provides a ton of variations, including several patents.

Before the advent of computers, and possibly still now, planimeters were/are widely used in Naval Architecture to calculate vessel characteristics such as displacement, center of buoyancy and such, directly from drawings. There was even a bizarre contraption to directly plot stability curves (righting moment vs. heel angle). I have no idea how it works.

Cheers,
Joe

[Farmer Geoff]

In the 1960's and 70's, the amount of rice one could grow in MIA and other irrigation areas was restricted to a certain area whereas nowadays it is restricted by the amount of water one has rights to. When restricted areas applied, aerial photos were taken and the irrigation regulators used a planimeter to measure the area of rice that a farmer had. Farmers with allowable areas of 50 acres would gamble on the planimeter's accuracy a bit and perhaps plant 52 acres and keep their fingers crossed but if they were found to have too much then they would have to stop irrigating the excess and therefore waste some establishment costs. So the planimeter was their equivalent of our speed radar.

[Stustoys]

While rescuing a Planimeter that had mistakenly found its way to Perth of all places and returning it to its rightful place in the tool capital:D, I came across this.

Only $395! a bargain compared to the $980 it would cost you new from NZ.

Trig Instruments New Zealand - Koizumi Placom KP90N Planimeter (http://www.triginstruments.co.nz/catalog/product_info.php?products_id=278)

Stuart

[Mobyturns]

they we pretty standard kit in any respectable surveying firm & for cartographers, along with cartometers, Ohdner calculators & Chambers 7 figure logarithmic tables. :oo: some of us even used them!

Very long time since I used these along with wash brushes & ruling pens on high quality linen paper maps.

[Stustoys]

Been shopping again, now l'm all set up to measure areas now. Just got it today, its been around the block a few times by the look of it. a good clean should do wonders for its appearance though it seems to function just fine.
Anyone got any ideas what the part in the second picture is for?

Stuart

[franco]

B
Anyone got any ideas what the part in the second picture is for?
Stuart

Used to draw a circle of known area, i.e 100 square cm. so you can calibrate the planimeter for the job in hand and work out the conversion factor for whatever units you want to work with - see post #6.

Hope you have a steady hand! Up to about the sixties, each year the areas of hundreds of individual sugar cane paddocks at each Queensland sugar mill which had been newly planted with sugar cane had to be surveyed using a chain and compass, and the results hand plotted onto tracing paper. The areas then had to be measured with a planimeter. We had to get three successive results differing by less than 0.003 before the area would be confirmed. Since this was at the time done in the middle of the tropical wet season with the temperature around 35 degrees and very high humidity, and lacking air conditioning, your hands tended to sweat and leave greasy marks on the tracing paper. This would cause the integrating wheel to slip and give a false reading. Much sweat on the paper also caused the paper to stretch, once again affecting the result.

This was one area where I was very happy to see the advent of computers!. They are an interesting instrument though.

Frank.

[Stustoys]

Hi Frank,
I thought it was something along those lines, but the big VEE at the pencil end had(and still has) me scratching my head a little. At least I'm sure what it is now

Thank you

Stuart

p.s. Yes it was purchased for its interesting factor rather than any thought that it would get much use.