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knowledge is power
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Thought it might be a good idea to start collecting some of the specific formulas and best "Rules of thumb" in one location. I know there are tons of things that could be stuck here, so maybe we put the resulting list into a PDF later? Here are a few I think I've seen on the boards already:

1 Foot Height = 0.434 PSI (Gravity feed pressure)

Ideal Sewage pipe decline 1ft:4 inches of rise.
(to little and backed up sewer, to much and solids get stuck)

Basic Electricity Chart
E=IxR
E=P/I
E=Squareroot of (PxR)
I=E/R
I=P/E
I=Squareroot of (P/R)
R=E/I
R=P/I-squared
R=E-Squared/P
P=IxE
P=I-squared x R
P=E-Squared/R
 

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One atmosphere of air pressure at sea level is 14.7PSI.
Every 33 feet of depth is one atmosphere.
Salt water causes you to be come more buoyant than fresh water.

Ideal blood pressure of the average adult is 120/80 with a pulse of between 60 to 90 and respiration between 12 and 20. Pupils should be evenly reactive to light and the person should be able to articulate the date, where they are/where they are going, and who they are. Anyone suspected of a spinal injury should not be moved without the proper equipment and stabilization.

Your engine oil should be changed every 3k to 5k miles or before a long drive. Your (stock) tires should be properly inflated as per the GVW sticker located under the gas cover, in the drivers door jam, or in the included service manual, NOT WHAT THE TIRE SAYS IT CAN HOLD. Be sure to also monitor your transmission fluid, coolant (if equipped), break fluid, power steering fluid (if equipped), and any other ancillary fluid levels of your vehicle.
Tires have a tread wear indicator on them to show when they should be replaced.
Generally speaking, manual transmissions are stronger than an equivalently built automatic transmission.

There is a ton more but this is just whats off the top of my head, need to go to work.
 

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Pi, (3.14159), works pretty good on earth, but it is not a universal constant.
 

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Anarchist/Animist Primate
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I highly recommend picking up a small book called The Pocket Ref. It has all that and more...

Amazon.com: Pocket Ref 4th Edition (9781885071620): Thomas Glover: Books

Here's the description: "The concise all-purpose pocket-sized reference book featuring abundant information on many subjects, hundreds of tables, maps, formulas, constants and conversions. If you need to know it, it is in this book!"
 

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Geometric formulas

So if you don't have these memorized, HS must have failed you lol.

I will not fail you.:thumb:

Keep in mind a couple of things. Without these formulas below you cannot estimate even basically, ANYTHING that involves building ANYTHING, including prices and amounts of materials.

Log.......


pi = = 3.141592...)
Areas

square = a2

rectangle = ab

parallelogram = bh

trapezoid = h/2 (b1 + b2)

circle = pi r 2

ellipse = pi r1 r2

triangle = (1/2) b h

equilateral triangle = (1/4)(3) a2

triangle given SAS = (1/2) a b sin C

triangle given a,b,c = [s(s-a)(s-b)(s-c)] when s = (a+b+c)/2 (Heron's formula)

regular polygon = (1/2) n sin(360°/n) S2
when n = # of sides and S = length from center to a corner

Volumes

cube = a3

rectangular prism = a b c

irregular prism = b h

cylinder = b h = r2 h

pyramid = (1/3) b h

cone = (1/3) b h = 1/3 r2 h

sphere = (4/3) r3

ellipsoid = (4/3) pi r1 r2 r3

Surface Areas

cube = 6 a2

prism:
(lateral area) = perimeter(b) L
(total area) = perimeter(b) L + 2b

sphere = 4 r2
 

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I see a bad moon arising
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Pi, (3.14159), works pretty good on earth, but it is not a universal constant.
Wait. :xeye: Why is Pi not a universal constant?

(Or are you referring simply to the rounded value that you listed?)

Just curious.

============================================================

Ideal Sewage pipe decline 1ft:4 inches of rise.
(to little and backed up sewer, to much and solids get stuck)
I think the ideal slope is 1/4" per foot, not 4" per foot.

============================================================

My addition to the list: 3:4:5 triangle for laying out right angles. Measure 3 units along one side, 4 units along
the second side. Adjust the angle between the two sides such that the distance between the 3 unit and 4
unit measurement comes out to exactly 5 units. = 90 degree angle. Useful for laying out footings, squaring up
walls, etc.
 

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Wait. :xeye: Why is Pi not a universal constant?

(Or are you referring simply to the rounded value that you listed?)

Just curious.
It depends on how you define Pi. If you do so strictly mathematically, you can say 3.14159..........

If you do so based on geometry, the ratios do not work universally, throughout the universe. The Universe is not homogenous, it has lumps and bumps that alter the geometric value of Pi.
 
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Thinking outside the box
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Does this include Murphy's law......

When you need screws there is always X-1 in stock.

A dropped wrench will always fall where it can do the most damage.

After you tightened down the 16 screws holding down the cover, you discover that you forgot the gasket.
 

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The easiest formula to remember: E=MC^2

I mean, you throw that one out and suddenly everyone thinks you're a freaking genius.

But in all seriousness. I learned a pretty interesting rule of thumb in terms of cooking a few weeks ago, and it really helped with my grilling.

To check the doneness of your meat, you lightly put the tip of each finger on your left hand to your thumb. With your right hand press the meaty part of your thumb. Compared with your meat, you can determine the doneness through this chart:
Index finger to thumb: rare
Middle finger to thumb: medium rare-medium
Ring finger to thumb: medium-medium well
Pinky to thumb: Well done

I tried this on chicken, and it came out exactly as I wanted it, without overcooking it.
 

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The easiest formula to remember: E=MC^2

I mean, you throw that one out and suddenly everyone thinks you're a freaking genius.

But in all seriousness. I learned a pretty interesting rule of thumb in terms of cooking a few weeks ago, and it really helped with my grilling.

To check the doneness of your meat, you lightly put the tip of each finger on your left hand to your thumb. With your right hand press the meaty part of your thumb. Compared with your meat, you can determine the doneness through this chart:
Index finger to thumb: rare
Middle finger to thumb: medium rare-medium
Ring finger to thumb: medium-medium well
Pinky to thumb: Well done

I tried this on chicken, and it came out exactly as I wanted it, without overcooking it.
I was just gonna pass on this, but I can't.

That's dumber than a box of rocks.
 

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Bravo Zulu
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Ideal Sewage pipe decline 1ft:4 inches of rise.
(to little and backed up sewer, to much and solids get stuck)
That should be fall, not rise. Sewage doesn't like flowing uphill. ;)

Another one to remember, pythagoras' theorem. 3, 4, 5. The sum of the square of the length of two sides of a square, rectangle or oblong equals the square of the hypotenuse.

Use a stick to work out the length of a tree once it's fallen. Hold the stick at a distances from your eye so that you can measure the tree against the stick, then lay the stick over. Where the ends of the stick appear to be is where the tree will be.
 

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I highly recommend picking up a small book called The Pocket Ref. It has all that and more...

Amazon.com: Pocket Ref 4th Edition (9781885071620): Thomas Glover: Books

Here's the description: "The concise all-purpose pocket-sized reference book featuring abundant information on many subjects, hundreds of tables, maps, formulas, constants and conversions. If you need to know it, it is in this book!"
That is a great reference to have, I've worn the cover off mine.
 

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I was just gonna pass on this, but I can't.

That's dumber than a box of rocks.
Oh? I thought it was quite ingenious, as I have had a couple of bouts with food poisoning from undercooked meat, and getting food poisoning in a SHTF situation could mean a death sentence. It works, and it makes for more palatable cooking. Unless, of course, you like eating charred meat just to be sure all the bad microbes are killed.

So, please enlighten me as to how it is "dumber than a box of rocks".
 
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