Garmin Xero C1 gets the SD wrong
- Thread starter legi0n
- Start date
75 yards for most calibers .243" +
I did a 30 round string with a 223 this afternoon. 19.1 SD using sample , 18.8 SD using population......
this is ok
30 rounds is a good sample
try 3 or 5 rounds (which is the usual sample) and see the difference
just for fun I ran the diff between the 2 SD methods
the formula is
which for n=30 computes to 1.017 (1.7%)
todbartel's difference is 19.1/18.8 = 1.016 (1.6%)
darn close I would say
remember kids: 30 rounds is a good sample; 5 is not
the formula is
which for n=30 computes to 1.017 (1.7%)todbartel's difference is 19.1/18.8 = 1.016 (1.6%)
darn close I would say
remember kids: 30 rounds is a good sample; 5 is not
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Yes!
by the formula, for 4 shots, the sample/population = 1.154 (15.4%)
your numbers 21.6/18.7 = 1.155 (15.5%)
thanks for the data
So here's a chart of the data:
A histogram that I had hoped would be smoother:
Here are the stats:
| Mean: | 2771.642 |
| SD: | 13.12501 |
| Skew: | 0.071484 |
| Kurtosis: | -0.10632 |
And here's the raw data: https://nextcloud-fi.webo.hosting/s/Fqw8ZQAQnAZcTN2
It got warmer as the day went on (from about 5C to 22C), and this affected velocity as shown in the trend line.
Visually, the histogram is quite lumpy, suggesting more data required. While there is a mildly positive skew, it isn't significant.
PS: numbers from my newly-acquired LabRadar LX.
PPS: shot #1 was a cold barrel
Yaaaay! Great discussion on statistics! Now do the people that cling to shooting single shots in a ladder, and think that a plateau is a 'node' and that is what they should use as a powder charge. It's a statistical embarrassment that that method has gained so much attention in the shooting community.
Lets get something straight, the thread title is misleading, Garmin doesn't get the SD wrong, it gets it differently. A person in statisicts would tell you the difference is statistically insignificant. This thread is akin of how many spirits can dance on the head of a pin, or what kills faster, .308 or .30-06. It is all a matter of opinion. Over 40 years ago when I used to compete in 1000yrd matches in the US there weren't a lot of chronographs around, SD and ES meant little. We worked up a good load and learned to dope the wind etc and sometimes were rewarded with an 8" group at that distance - how did we ever achieve that without knowing each fired rounds and future rounds SD.......
Indeed, the difference becomes insignificant on really large samples.
but for the usual 3 or 5 shot samples, the difference is 22% and respectively 12%
I wish for a 12% pay increase...
like Tom Morrison said it, it looks like a marketing move
You mean the difference becomes insignificant on meaningful sample sizes. Everyone who knows anything about statistics knows a sample size of 3-5 is only useful if your population is very small - which is not the case for a firearm that is good for thousands of rounds.
If you know enough to argue which SD to use, and you're still using 5 shots to determine your SD, that's a user problem not a device problem IMO.
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yes Suther you are right on all points.
I was unable to convey my thoughts: most people who buy a Garmin don't know any of these. They just say "look what a good SD I'm getting" based on 3 or 5 shots.
Garmin could have used the correct method and didn't. Where it would matter is ELR shooting when trying to figure out hit percentages, or just for correctness in general.
As legi0n says, most people only do a few shots and take the SD from there.
Most people aren't ELR shooters though.
I'll quote myself: "Garmin could have used the correct method and didn't." And some people are ELR or just LR - these are the people who disproportionally buy chronographs.
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