acronyms

[NWFLYJ]

Could someone help me with this?

311284, 35.0 grains, av 1697; es 91, sd 28; 10 rounds scattered to 2.8".

av= average?

es=?

sd=?

Thanks Mark

[giz189]

av = average

es = extreme spread

sd = standard deviation

[NWFLYJ]

Thanks for the reply,

What is extreme speed, what affects it, the higher the better?

What is stardard deveation, what affects it, the lower the better?

Are the values being generated by the crono?

Thanks again Mark

[oneokie]

Extreme Spread, the difference between the lowest velocity and the highest velocity in a particular shot string. Lower is better.

[NWFLYJ]

Thanks Mark

[geargnasher]

Standard deviation took about eight weeks of class for my statistics professor to explain, and I've had a few night's sleep and an adult beverage or two since then. Suffice it to say that it is basically a way of determining how close the data was to the center of the bell curve of a data graph, or a way of measuring the relative accuracy of a data set.

Gear

[Buckshot]

............The 'SD' (Standard deviation) is used in statistics and probability theory. My wife had that junk in college and tried to scientificly explain it to me once until I hit my knees and begged her to stop, before my head exploded.

It's simply a number derived (I don't know how it's derived) to show how much variation there is from the "average". A low standard deviation indicates that the data points tend to be very close to the mean/average, whereas high standard deviation indicates that the data is spread out over a large range of values. People who do this stuff also have special names for some things, like you and I would say "A 10 shot group", these boffins would call it a 'Population'.

If you had a string of 5 shots that gave:

2304
2175
2398
2275
2197

Your 'average' velocity would be 2270 fps and you'd have a large SD as the velocity spread from the average for each shot would be:

34
95
128
5
73

Now you and I would probably be able to look at the target and tell our SD (and more importantly the load) wasn't worth rancid owl sweat without bothering with a number for our SD. We would simply live our lives happily trying to improve it never having HEARD of SD's. Now somehow or the other someone figured out how much better it would be to express our shooting embarrassment mathematically. These were people who had lots of time and nothing worthwhile to do, like inventing beer, BBQ, or banjos.

SD is used for comparisons with other things, groups, populations (stuff?) as the resultant numbers themselves are MUCH easier to compare then 10 shot velocity strings. SD's can also be represented as percentages of something or other, but I'm sure not the person to ask, I'm just mentioning another complication to it all :-).

If you have a chronograph that displays the SD for each string, you can use that number for comparison for follow on load developement. Of course for us shooters you can have a very low SD and a huge group out there. SD's in chronos' are only concerned with velocity. You can also use SD's if you graph your groups and don't mind doing the math. I'd rather simply look at them and either cry or smile.

...............Buckshot

[lwknight]

Buckshot , your right. That makes my head hurt too.

[fatnhappy]

Standard deviation took about eight weeks of class for my statistics professor to explain, and I've had a few night's sleep and an adult beverage or two since then. Suffice it to say that it is basically a way of determining how close the data was to the center of the bell curve of a data graph, or a way of measuring the relative accuracy of a data set.

Gear

standard deviation is basically the measure of a standardized normal curve. It's used to define the size of the curve in relation to the data sampling. It's real value is used to describe future probabilities based on historical performance and it does so very accurately.

oh yeah Buckshot.... the mathematical underpinnings for small batch statistical sampling and eventually statistical process control were pioneered by Guiness brewery.
So yes, SD was used to improve the quality of beer.

[Elkins45]

Is it correct to generalize and say that standard deviation is an average of how much each individual reading deviates from the average (mean) of all readings?

I understand why chronos generate a SD figure (easy for a computer to do since it has all the needed data) but I don't know how well it correlates to group size.

[felix]

Yes. ... felix

As the range to target increases, the "weight" of the velocity's SD increases within an equation for predicted group size. The equation must also include an SD for the angle of departure from the barrel centerline. However, this term would be a constant, rather than a variable based upon target distance within the equation. ... felix

Make your head hurt? Consider the math required to calculate the targeting a football field at 26 miles from a moving bench (ship). Yes, that is the accuracy obtained in real life: a football field. Amounts to 1.5 inches or thereabouts at a hunnert. ... felix

[Wayne Smith]

The State of New Hampshire has the largest lower house of it's Congress in the country, something like 430 members, drawn from the population of the state geographically. When the Board of Psychology was establishing the Certification of Psychologist law they wanted to use a standard of one SD above the mean score of the standardized national test given to canidates.

The Statistics Department of the University of New Hampshire advised the board to go with the mean. They stated that they could not adequately explain the concept of a standard deviation so that it would be understood by 430 diverse members of Congress, many of them farmers.

The Board of Psychology chose to go with the Mean.

[KYCaster]

The State of New Hampshire has the largest lower house of it's Congress in the country, something like 430 members, drawn from the population of the state geographically. When the Board of Psychology was establishing the Certification of Psychologist law they wanted to use a standard of one SD above the mean score of the standardized national test given to canidates.

The Statistics Department of the University of New Hampshire advised the board to go with the mean. They stated that they could not adequately explain the concept of a standard deviation so that it would be understood by 430 diverse members of Congress, many of them farmers.

The Board of Psychology chose to go with the Mean.



Hey, if congress critters can understand constitutional law and balanced budgets, then surely they could un...der.....stand............Ummm
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Never mind.
Jerry

[Echo]

I generated lots of headaches back in the day - as a Stat professor @ university level. But.

The SD can be well-thought of as the average deviation of the individual shots from the group mean. That's not really right, but it is a good way to conceptualize the meaning of the sd. Actually, it is the square root (RMS - Root Mean Square) of the average of the squared deviations (MSD - Mean Squared Deviation). The lower the sd, the less variability in the measure, whether it be of velocity or whatever. And remember - we are dealing with NUMBERS, not the actual occurrences. With a chrony, the numbers are exact enough for our purposes, since no human entered the numbers into a computer - humans make errors, such as transposing two digits, screwing up the detail. And there doesn't seem to be a perfect, or even near-perfect, relationship between sd and group size.

IMHO, EVERYONE should be required to take a class in basic inferential statistics. Politicians, and demagogues of all ilk, including college professors, will try to obfuscate the issue with arguments based on statistics.

(Occasionally one will run into a mass of data that has some numbers that don't seem to fit. These are called out-liers. The folks that use stat to obfuscate are called out-&-out-liers...)

We can thank Guiness for a product that will alleviate the brain-cramp brought on by a discussion of sd's, but we have to blame them (partly) for the problem itself, since it was their brew-master, named Gosset, who gave us the t-test. His employers wouldn't allow him to publish his discovery, since it would be revealing trade secrets, so he published anyway, using the name A. Student. The procedure is still known as Student's t-test.

And now is the time to seek out the other Guiness product.


(How's THAT for stirring the pot!)

[felix]

Ah, Echo. Stir the pot, eh? Well, so why stop at squares? Let's do cubes, quads, etc. Never mind, that would make Gosset's head hurt, and we can't have that. ... felix

[Maven]

"Actually, it is the square root (RMS - Root Mean Square) of the average of the squared deviations (MSD - Mean Squared Deviation)."

Echo, et al., My statistics professor made us do those calculations by hand, or by slide rule if you knew how to use one. This was in 1966, before handheld calculators and PC's. Come to think of it, all our statistics homework and tests had to be done manually. However in 1968, a branch of the university I attended, got an electronic calculator with grant $$$. It was as large as an IBM typewriter with a ~3" x 3" screen, cost $3k, and had a memory. That feature made complex calculations (Chi Squares) a breeze to do* and would have been just as handy with SD's.


*I was a research ass't. at the time and part of my job was checking my boss's calculations.

[fatnhappy]

"Actually, it is the square root (RMS - Root Mean Square) of the average of the squared deviations (MSD - Mean Squared Deviation)."

Echo, et al., My statistics professor made us do those calculations by hand, or by slide rule if you knew how to use one. This was in 1966, before handheld calculators and PC's. Come to think of it, all our statistics homework and tests had to be done manually. However in 1968, a branch of the university I attended, got an electronic calculator with grant $$$. It was as large as an IBM typewriter with a ~3" x 3" screen, cost $3k, and had a memory. That feature made complex calculations (Chi Squares) a breeze to do* and would have been just as handy with SD's.


*I was a research ass't. at the time and part of my job was checking my boss's calculations.

I used a chi² test to prove a point at work today. I might as well speak chinese. Blank stares all around.

[NWFLYJ]

RMS = Peak high and peak low X .707? or is that only in AC circuits?

[Echo]

RMS = Peak high and peak low X .707? or is that only in AC circuits?

That is an approximation, based on the assumption of the normal distribution of data points, but entirely valid for AC circuits.

Bring on the Guiness...

[Echo]

I used a chi² test to prove a point at work today. I might as well speak chinese. Blank stares all around.

Many stat texts don't even teach the chi-square test any more. I am pleased that it is still in use. You get a Way To Go!