The first thing you'll need to do is design the rule. There are places on the internet that have templates for circular rules, but I wanted to design my own. It turned out that in the process, I learned a lot about how slide rules worked. Anyways, I wrote a C code to produce a .svg file of the front and back faces, along with the interior pieces that hold the rule together while letting it slide around. The code is below, and the result is in "slide_stator.svg". The cursor is in "cursor.svg". I designed these files so that the rule could be cut out of acrylic with a laser cutter. I don't have my own laser cutter, so I had the guys over at

ponoko.com do the cutting for me.

Anyways, some notes on the design:

On one side (let's call this "side 1"):

* A log scale (inner)

* A C/D scale (sliding)

* A sine scale, in radians (outer)

On the other side (side 2):

* A K scale (inner)

* An A/B scale (sliding)

* A cosine scale, in radians (outer)

UPDATE: At someone else's suggestion, I'm also attaching .pdf versions of the templates, so people can just use card stock. Note that when you look at the files, the lines are very very thin. This is because the Ponoko folks need to have the templates in a certain format.

Thanks :)

I'm obviously going to have to break out my slide rule and find out...

"To use the slide rule as a vernier, one sets the right-hand index of the C scale directly over the 9 on the D scale; then for every ten divisions anywhere on the C scale there are 9 on the D scale. Thus the C scale becomes a vernier to read the D scale.........There is no reason why we must limit ourselves to tenths of a division. The slide rule vernier can be set to divide each division into five, eight, twelve, twenty, or indeed any convenient number of parts, according to which numbers on the C and D scales are originally lined up."

Quick example. Put the cursor over the "pi" mark on the D scale. Move the C scale to the left until one full division on the upper C scale exactly matches the interval between the 3.1 mark and the "pi" mark on the D scale. The right index of the C scale lines up near to 4.2 on the D scale. These are the next two digits, so pi =3.142. It is more work, but it gives you an extra digit of precision, with care. My eyes aren't so good, but in the photo I made, you might even care to estimate with greater precision a value close to 3.1416.

I'm looking for a slide rule that can be used in photography - one that you insert the flash number guide, the distance between the flash and the subject, and you read the aperture/speed/ISO (wow, there's a lot of variables on this one).

There's a discussion about guide number slide rule here:

http://photo.net/photography-lighting-equipment-techniques-forum/00UbPg

Can you point me some guide where I can learn about the calculation of rules? Thanks!

GN = distance * f-stop

but the wikipedia article says this only works for ISO 100. I couldn't find anything saying how the equation is modified for different ISOs. Anyways, if you're looking for something that does the above calculation, you can use any old slide rule: the C/D scale can do multiplication OR division, so if you wanted to calculate the f-stop from the GN and distance, you'd just do

f-stop = GN/distance

on the slide rule. Hope this helps!

Thanks for your answer.

I did some research on the topic, and found that when you increase the ISO, you must increase the f-stop. If your calculation points to f4 for ISO100 at a certain distance, you have to use f5.6 for ISO200, f8 for ISO400, f11 for ISO800, and so on (there's a sequence of f-stop and ISO).

I also found a page full of "exposure calculators". Now I only need to get inspired and do the work...

http://www.mathsinstruments.me.uk/page67.html

It attached to their thy so the pilot only needed one hand to use it.

I have been trying to find instructions on how to use it for about 25 years!

Can anyone help?

** Just saw the message from

about pilot shops... ??? Pilot shops? **fazgardMy traditional flat linear slide rule- which I still don't know how to work

properly, is aPicket Microline 140. Your link will definitely help me there.My circular slide rule which I would like to get to know

correctly, is aConcise No. 300. It is just a bit over 12cm in diameter, or about 4 7/8".This may sound stupid, but since the scales go round and round, I can't quite figure out how to apply anything from the tradional rule to the round version.

I have (never use now… ) a linear slide rule but will trade it for a circular one.

Very convincing.

You got my vote.

Fantastic project!! Plan on making several for my kids. You got my vote.

I'd love to see pictures once you make them for your kids!

(5 stars anyway!)

They have been around since before WWII and have all sorts of cool things built in to the scale for rates and unit conversion.

What fun we had before TI-83's!

Laser Bits - http://www.laserbits.com/index.php?main_page=index&cPath=76

(Apparently they are selling them in 3-packs now. $50)

Sign Warehouse - http://www.signwarehouse.com/c-ENIPI.html

-- Laserables 1/16 thick: http://www.signwarehouse.com/c-ENIPI-LAF.html

-- Heavy Metal 1/16 thick: http://www.signwarehouse.com/c-ENIPI-LY.html

Hope that helps!

Jerry

(I have an Epilog 35w laser)

Jerry

of course!