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    Re: Traditional navigation by slide rule
    From: Paul Hirose
    Date: 2016 Jan 08, 22:31 -0800

    On 2016-01-06 16:49, David Pike wrote:
    > My first one at school was one of those Faber Castells with the parallel 
    green background stripes.  How many other teenagers were seduced by those 
    green stripes which promised so much?
    Many think the Faber-Castell 2/83N is the greatest slide rule ever made.
    Unfortunately its trig scales are on the body. That's not optimum. Last
    year on the Yahoo slide rule discussion group I said, "Several times I
    have questioned the logic of placing trig scales on the body, most
    recently on the 8th and the 15th of July. I have yet to see anyone
    defend that arrangement with a worked example."
    That drew some responses! There were cases in which scales on the body
    were not a disadvantage. But in no case was there an advantage, and in
    the end I didn't change my mind.
    > I will send two photos of my most recent Blundell, a 401 REITZ purchased 
    from a Government Surplus shop in 2000 for 50p (75c).
    This shows the scale arrangement more clearly:
    A Rietz slide rule (named after German professor, I think) is an
    excellent basic slide rule, better than a Mannheim rule (also named
    after a person). The latter is more common here in the US.
    In trig computations the big problem with a Mannheim rule is that scale
    S covers two decades of sines (.01 to 1.0) but scale T covers one
    decade. I.e., S works with the A scale, while T works with D. This is
    awkward when a formula has sines and tangents. Try to work a Bygrave
    sight reduction on a Mannheim rule and you'll see what I mean.
    Rietz slide rules split the old 2-decade S scale into separate scales ST
    (for the small angles) and S. Thus they work smoothly with each other
    and the T scale. This set of three trig scales became standard when the
    slide rule reached maturity in the mid 21th century. (I don't know if
    the arrangement originated with Rietz, however.)
    It's true that some rules have a second T scale which goes from 45 to
    ca. 84 degrees. On Yahoo I once voiced a strong preference for that
    arrangement, and wondered why so many flagship slide rules were content
    with the single T. (The K&E Deci-Lon is one example.)
    I later backed off from that position. Single vs. double T scale is not
    a big deal, and actually I appreciate the elegance of the single T.
    If David flips the slide of his Blundell 401 over to the trig side, all
    the necessities are there. The only missing feature is double numbering
    on the S and T scales, e.g., red 70 and black 20 on the same graduation.
    That's convenient but not necessary.
    The Pickett N4 has been mentioned. As far as I know, its count of 34
    scales has never been exceeded by any production slide rule.
    As a teen I wanted an N4 in the worst way, and eventually got a 5" / 10"
    twin pack as a gift. A lot of people must have been like me, as the N4
    is common and affordable nowadays on the used market. Its sibling N3
    must have sold in much fewer numbers. However, I now think the N3 the
    better rule. It lacks the N4's hyperbolic scales, but I never used them
    except to work the problems in the manual. As for the "double base" that
    Pickett bragged about on the N4, if you ask me for an example to
    demonstrate its power, uh...
    A significant irritation on the N4 is that its numbers are squashed down
    onto the scales. In the photo, top image, top scale (LL1), note 1.006,
    1.007, etc. And also note how the cursor blocks your view of the
    numbers. The red numbers on the inverted scales are bad too. Look at 9,
    8, 7 on CIF. Ugly! That comes from trying to crowd too many scales onto
    a slide rule.
    The slightly less deluxe N3 is much more readable.
    However, my favorite slide rule is a late 1950s K&E Log Log Duplex
    Decitrig. It's a plastic rule, well equipped for science and
    engineering, but utterly commonplace, the slide rule equivalent of a
    plain gray tabby cat.
    It's strange how your life takes unexpected turns. As a teenager
    shopping for my first "real slide rule", the K&E was my second choice in
    case the Pickett was too expensive. It was a big step up from my
    Sterling Precision beginner's rule, though no match for the power of the
    mighty N4.
    Well, I got my dream slide rule, eventually decided its design flaws
    made it not so dreamy, and realized the K&E was what I should have
    bought in the first place. Of course if I'd done that, I would have
    ended up buying an N4 anyway to replace the "interim" K&E. Sooner or
    later I had to make that mistake in order to learn. What I have learned
    is the power of a slide rule comes mainly from the user.
    p.s. The top quality slide rule images one sees online usually come from
    flatbed scanners. From time to time on the Yahoo group there are
    discussions on which scanners are best for this.

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