Wow very nice! Is that card stock you're using there? Your cut circles look damn near perfect to me! Did you use regular old scissors?

As an aside, having never used a slide rule before and not being the most mathematically adept person out there, I was up until 2am scoping out the web for a user friendly guide on slide rule operations. I came across this site at UC San Diego where a professor holds a seminar on slide rule operations. How about that! He has a 13 MB .pdf file of his PowerPoint presentation here Good stuff for beginners.

What is meant by 20 degrees between the 4 and the 7??

I have a proper engineering slide rule infront of me (my fathers from years back), and no matter how I move it so that the slide moves 20 degrees acording to the S table I get results that are at least a degree if not more different to yours. i.e 22 degrees at 7000 metres and 41 degrees at 4000 metres.

How do you calculate that 20 degrees onto the slide rule??

My brain is fried. Maybe it's because I don't remember my trig from YEARS ago or that I just suck at math but I'm getting inconsistent results with my rule. I need an idiot's guide to these things.

Yep, it's cardstock. I use it for making my own QSL cards. Every layer is laminated, including the transparencies. That makes it more rigid, and it protects the print.

As for the cuts, yes, I use regular old scissors. I just cut right along the lines, and I take my time. For the actual circular slide rule, I got my compass from high school and drew a circle on the back of the cardstock that had the slide rule printed on it, centered on the pivot, that I pre-punched. Then I just cut along the line...

I did it while my 3 year old son was in for a nap. Took about 45 minutes total, being careful, but I already had the cursors from a previous incarnation of the slide rule, so that saved me some time.

I'll have to check those links out, sounds cool. :up:

I'd have to see it to know for sure, but I have three rules, two I made and one that was manufactured, and they are all in agreement (within a certain amount).

When I align 23 degrees on the S scale to the second 4 on my A scale, then 43 degrees on the S scale lies directly below the 7 on the A scale.

You might have to use the D (or C) scale with the S scale on your rule, as I noted in my instructions the rule I was using has an S scale that is "double", ie., it goes from just under 40 minutes all the way up to 90 degrees, so I *HAVE* to use the A scale.

If you have a normal S scale that goes from just under 6 degrees up to 80 or 90 degrees, you can't match it against the A or B scale, you have to match it against the C or D scale.

Hope that helps.

EDIT: If you have a normal S scale and the target is coming close to right at you or moving almost directly away, you might have to use the ST scale, which would go from less than one degree up to about 5.5 degrees, give or take, against the C or D scale.

It just takes some practice. I fooled around with it for at least a week before I posted those instructions.

Trust me, I'm wearing a silly medic hat!

Here is another nifty cardstock / lamination project:

Do a GIS for 'maneuvering board'. Print it out on cardstock, then laminate it.

You can then use a fine point erasable whiteboard marker to keep track of contacts, and to erase it just use a paper towel or toilet paper.

(I feel like Kapitanleutnent Martha Effin' Stewart today)

I still can't get it:dead:, my biggest problem is i still don't understand what you mean by 'twenty' degrees. Do you meant I have to move the slide rule two little ticks in one direction? none of which add up to twenty in value, or that I have to move the slide rule to a certain 'value' of twenty indicated by the slide.

This step is also not very well illustrated by your photo as from what I can see you have not moved the slide by 'twenty' by either the ticks or value:doh:.

I attempted to use this method trying both the value and the tick method but both gave me angles of bearing that were clearly too low i.e: 025 when the target was clearly well above an AOB of 045.

Thanks for Writing this article by the way, I've been hunting round trying to find such an article for a while now since I knew dad still had his old slide rule hanging around.:up:

OK, the difference between our first bearing of 65 degrees and our second bearing of 45 degrees is 20 degrees, right?

Now, at the beginning we don't know the target AOB with any certainty, but we have a 'guesstimate' from looking at the ship. So lets say that we 'guesstimated' that the AOB was 50 degrees when the target was at observation B (Distance 4000, relative bearing 45 degrees).

You would slide the S scale so that the 50 is underneath the distance of observation A, or in our example aligned with the 7 on the A or D scale as appropriate.

We then slide the cursor down 20 degrees on the S scale (which would put us on 30 degrees on the S scale). On the A or D scale, it reads 4.56, which isn't right. It should land on the distance to observation B, which is 4000 (4 on the slide rule).

That means our AOB estimate was off. So, we try an AOB of 45 degrees. Aligning that with the 7 (distance for OBS A), we find that 20 degrees less than 45, or 25, lands at right about 4.2, which is close to our expected 4.0 value.

So, we fiddle with the slide until we figure out that when 23 degrees is under the 4, 43 degrees is under the 7. That is our 20 degree difference.

Interestingly, the AOB for observation B, which we originally estimated to be 50 degrees, but it turned out to be 43 degrees, lies underneath the distance for observation A.

Also, note that the AOB changes from observation A to observation B by the same amount the bearing changes: 20 degrees.

Anyway, to get the distance the target traveled, we then slide the cursor down to the 20 degree mark on the S scale, and away you go from there.

Hopefully, that helps. Let me know if you need more.

This thread makes me want this.

Hmmm....now, how to convince the wife that a $100 slide rule is a needed component...

Thanks for the info. I have gone insearch of one that I had. It used to be my grand fathers' and would be great to be able to use it. Thanks.

ah, that's exactly what I was doing wrong, thank you, I've got it figured out now... now to use my new found skills on some enemy subs

:)

Glad to hear it!

It isn't really an intuitive process until you learn the why's and wherefore's of slide rules, but once you understand how they work you can do it pretty quickly.

:up:

Glad to help.

Well I'm feeling a bit more comfortable practicing your example in this thread but over in this thread you gave a different example where the difference in bearing checks was only 7 degrees. I'm having a bit of trouble duplicating your results for that problem.

For example, in the problem listed in this thread where the bearing difference is 20 degrees, I start by moving the hairline to 4 on D scale, slide the 20 mark on S until it's on top of 4 on D, count how many degrees I have between 4 and 7 on D scale which comes out to 17 degrees on the S scale - I'm off by 3 degrees. So move the hairline back to 4 on D and move the S scale 3 degrees which gives me 23 degrees on 4 and 43 degrees on 7. I now have 20 degrees between 4 and 7 and like you indicated I now have the AOB for those two bearing marks.

I'm just having trouble replicating those steps above to match up 7 degrees between the two bearing marks.