What does "engineering accuracy" mean to you?

Discussion in 'Hydrodynamics and Aerodynamics' started by Leo Lazauskas, Feb 4, 2013.

  1. jehardiman
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    jehardiman Senior Member

    Now there I see the beginnings of a master's thesis. A few years study of the results at Henley and I bet I could correlate socks and/or ties to speed. Even make it into an award paper for The Journal of Irreproducible Results.
     
  2. murdomack
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    murdomack New Member

    I've totally forgotten how to do logarithms, yet I must have spent six or seven years doing them every day. Someone handed me a slide rule a few years ago and it was like a Rubik Cube to me.

    Funny thing is I've just done a Sqr Root calculation by hand from memory. I must have been paying attention the day we were taught that:rolleyes:
     

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  3. michael pierzga
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    michael pierzga Senior Member

    Holy Mackerel ...A slide rule !!!!!!!!!!!!!


    Id love to find my old slide rule . It must be hiding somewhere.

    It was my best friend when solving the celestial navigation triangle. At school I didn't have enough money to afford a scientific calculator. They were expensive.

    Im going to find that slide rule and refresh my mind.

    http://www.johndcook.com/blog/2009/09/07/why-spherical-trigonometry/
     
  4. daiquiri
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    daiquiri Engineering and Design

    When I was around 10 yrs old my father, an ex ship master, taught me how to use a slide rule, and also explained me how the celestial navigation works. The brain of a 10-yrs old kid is like a sponge for info, it absorbs everything with almost no effort. And I remember that it was all so clear to me.
    Now, I don't remember anything of it. Not even how to use a slide rule, though I'd spent some great time discovering secrets of math with the help of it.
    What a shame. :(

    From that link of yours, Michael - an interesting thought:
    "I think one of the things we are doing today is forgetting how we got where we are using certain fields of mathematics and relying too heavily on technology that can easily fail us."
     
  5. Petros
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    Petros Senior Member

    A slide rule is obsolete, an inexpensive calculator is more accurate and cost less and takes up less space. It is just not necessary to have a slide rule anymore.

    When I was in engineering school in 1977 the scientific calculators were coming down in price, both my older sister (studying physics) and my dad needed slide rules. I thought it was a good "back up" to the early and costly calculators, I taught myself how to use one and would sometimes use it for my homework. But one of my collage professors set me straight with those words above in 1977! When just about every electronic device we now own have built-in calculators, what that mean for us today?
     
  6. tom28571
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    tom28571 Senior Member

    When we got our first calculators at work in about 1972, it was an HP "reverse Polish" unit that we had to store in a secure unit locked to our desks because of the cost. A calculator can give you a garbage answer if you are not keeping up with the probable outcome. That was not an issue with a slide rule because you had to keep up with the calculation. Still have my trusty K&E but have not used it in at least 30 years. Most of my design work was done with that very ingenious instrument.
     
  7. Petros
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    Petros Senior Member

    If you have not used it in 30 years, I guess you do not really need it.

    garbage answers can come out of slide rules too. Neither calculators, nor computers, are substitutes for understanding what you are doing, the math involved and how it is affected when the different variables change. These are simply tools to speed up the process, not a replacement for knowledge.
     
  8. daiquiri
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    daiquiri Engineering and Design

    I agree that slide rules are obsolete, slow and less accurate than a scientific calculator. What I meant to say, by quoting that phrase, is that it is a pitty to see that an important part of general scientific knowledge, tools and methods is being lost because it is no longer competitive with high-speed electronic devices we have today. It still remains a scientific knowledge, and a cultural heritage. Besides being an excellent brain trainer.

    Another important knowledge which is disappearing is the calculation with pen and paper. How many of you guys are able to calculate a square root of a random number, without using an electronic calculator? I am not. Yet, I was able to do it some 25 yrs ago.

    Anyways, looks like there's hope for slide-rule nostalgics. :) I've just found two great apps for iPhone and iPad (I'm pretty sure there are versions for Android too) which simulate slide rules, and also teach you how to use them. And they are both free:
    - Pocket Slide Rule, by TestTubeGames (this one has a more complete double-face slide-rule)
    - Slip Stick, by Timothy Scott (this one has a better tutorial).
    :)

    Cheers
     
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  9. Number4

    Number4 Previous Member

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  10. CDK
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    CDK retired engineer

    Of course it's obsolete and of course nobody a slide rule anymore, but it did give us some insight modern students lack.
    It taught us and visualized that multiplying and dividing becomes adding and subtracting when you replace integers by their logarithms.

    I also wanted to make the point that a slide rule needs no battery, because the calculator in my boat is dead as a doornail from moisture corroding the innards, but my slide rule has swollen and doesn't slide anymore.... So that makes no difference.
     
  11. latestarter
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    latestarter Senior Member

    I am fast approaching the stage where it is easier to remember things from 40 years ago than what happened last week ;) this is the method I was taught.

    Say 594623
    split it into a number and 10 to the power of even number ie 59.4623 x 10 to 4th power

    59 is between 49 and 64 so roughly square root is 7.5, square root of 10 to 4th power is 100.
    Divide 594623 by (7.5 x 100) = 792.83
    add 750 to 792.83 divide by 2 = 771.41

    Divide 594623 by 771.41 = 770.82
    add 771.41 + 770.82 divided by 2 = 771.11

    repeat until accuracy required is achieved.
     
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  12. michael pierzga
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    michael pierzga Senior Member

    I still use my old Speed Time Distance wheel. fast and since its visual, its not prone to incorrect entries when navigating. Very usefull for routing when projecting a course or future EPs onto a Grib file weather chart . Always wanted one of those Beautiful Weems and Plath speed time distance slide rule divers.

    Since no one " navigates " anymore...prefering to simply watch their little boat icon move across chart plotter screen while glancing at the " when we gonna get there " numbers, it would be wise to pickup a nautical slide rule or navigators wheel before they go extinct.

    As far as I know the plastic sextant is still available. Very nice 50 euro tool. Nautical almanacs are virtualy unattainable

    http://www.starpath.com/catalog/accessories/1840d3.htm
     
  13. daiquiri
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    daiquiri Engineering and Design

    Very good, thanks. I am pretty sure this method is different from the one I was taught at school, but it is definitely an easy to remember one. Looks like it's based on the bisection iterative method.

    By the way, this thread has set up a process of hand-calculations here... I have dedicated this morning to the refreshing of my skills in hand-calculations, in particular divisions and square roots (with your method Latestarter - thanks). It's better, more funny and more useful than some board games. ;)

    Cheers
     
  14. daiquiri
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    daiquiri Engineering and Design

    Hell, I don't even know what I am looking at there - yet I can design a small airplane... :eek:
     

  15. Number4

    Number4 Previous Member

    Thanks latestarter!
    That took me straight back to a class room in 1984!
    I have been having flashbacks all morning now.
     
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