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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Two different SD's. Which one is correct?
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<blockquote data-quote="Hugnot" data-source="post: 2974386" data-attributes="member: 115658"><p>Great start with the nice Magneto Speed! Save data, then shoot 10-15 more. I save my data on PC & use spread sheet to develop it. Having 3 or 4 times more data will provide a better assessment. I don't have a clue of what happens inside that tiny chip jammed inside a one function button box with a 9-volt battery.</p><p></p><p>Get a good spread sheet like:</p><p></p><p>[URL unfurl="true"]https://www.openoffice.org/?lang=en-US[/URL]</p><p></p><p>Transfer crony data to spreadsheet, run analysis without going on-line, use canned stat functions like VAR & SD, save files, backup using One Drive.</p><p></p><p></p><p>[ATTACH]521284[/ATTACH][ATTACH]521285[/ATTACH]</p><p></p><p>Note, the average displayed using the tiny Magneto speed display is truncated to a whole number - inadequate. The average should be displayed as a fractional number having more precision, like 2978.667. Displayed individual fractional velocity values are sort of witless.</p><p></p><p>The variance is calculated by adding succession of values of the square of each velocity minus the average of all velocities, then dividing that sum by the number of cases.</p><p></p><p>The SD or standard deviation is the square root of the variance.</p><p></p><p>At this point it can be seen why subtracting each velocity by 2878.667 then squaring it then adding a succession of results would be different than subtracting each velocity by 2879 then squaring it then adding the results.</p><p></p><p>3 cases, TVal. = 2.776, est. Var. = 1.333, 12 cases TVal. = 2.145. est. Var. = .970. Yes, more data is better.</p><p></p><p>Suppose upon shooting 3 more 3 shot stings having velocities of 2978, 2980 & 2978 the average would be 2978.66, unchanged but more cases. The spread & SD would be the same but having more cases (a lower 95% probability T val.) an improved projection of velocity averages of highs & low should a big batch of ammo be produced. Mean differences less.</p><p></p><p>Think of a nice pointy bell-shaped short tail curve No need to discard data - just add data.</p></blockquote><p></p>
[QUOTE="Hugnot, post: 2974386, member: 115658"] Great start with the nice Magneto Speed! Save data, then shoot 10-15 more. I save my data on PC & use spread sheet to develop it. Having 3 or 4 times more data will provide a better assessment. I don't have a clue of what happens inside that tiny chip jammed inside a one function button box with a 9-volt battery. Get a good spread sheet like: [URL unfurl="true"]https://www.openoffice.org/?lang=en-US[/URL] Transfer crony data to spreadsheet, run analysis without going on-line, use canned stat functions like VAR & SD, save files, backup using One Drive. [ATTACH]521284[/ATTACH][ATTACH]521285[/ATTACH] Note, the average displayed using the tiny Magneto speed display is truncated to a whole number - inadequate. The average should be displayed as a fractional number having more precision, like 2978.667. Displayed individual fractional velocity values are sort of witless. The variance is calculated by adding succession of values of the square of each velocity minus the average of all velocities, then dividing that sum by the number of cases. The SD or standard deviation is the square root of the variance. At this point it can be seen why subtracting each velocity by 2878.667 then squaring it then adding a succession of results would be different than subtracting each velocity by 2879 then squaring it then adding the results. 3 cases, TVal. = 2.776, est. Var. = 1.333, 12 cases TVal. = 2.145. est. Var. = .970. Yes, more data is better. Suppose upon shooting 3 more 3 shot stings having velocities of 2978, 2980 & 2978 the average would be 2978.66, unchanged but more cases. The spread & SD would be the same but having more cases (a lower 95% probability T val.) an improved projection of velocity averages of highs & low should a big batch of ammo be produced. Mean differences less. Think of a nice pointy bell-shaped short tail curve No need to discard data - just add data. [/QUOTE]
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Two different SD's. Which one is correct?
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