Garmin Xero - update

[gregmark24]

Essentially all the N-1 denominator is doing is adding in variability. Just on a very basic logical level, if you're planning on using the data to decide to pick a recipe to make more ammo, then it's logical to conclude there will be more variations in your long term data. I think most anyone can agree that if you take a 5 round string, test it, then make 200 rounds....that 5 round string is most of the time going to have smaller numbers than 200. So, utilizing N-1 gives you a more realistic idea of what that variation is going to look like.

However, if you are testing all the ammo that will ever be made in a recipe, then you don't need to add in that variance. If you load 500 rounds and run them all over a chrono and will never make that ammo again, there's zero need to add in the -1.


I would challenge anyone on either side of the debate though. Show how using either P or S would be detrimental to your ammunition or loading.

I.E. give an example where shooter A always uses STDEV.P and shooter B always uses STDEV.S and give examples and data why either shooter A or shooter B would produce better ammo or perform better shooting.

That would be the ultimate way to prove either is "right" or "wrong." Show how one of the shooters would have a disadvantage to the other.

I contacted Garmin about the STDEV.P vs STDEV.S what, two weeks ago? I've never gotten a response; that's really disappointing.

 

[Dthomas3523]

@Dthomas3253, makes sense now that I think about it. Shooting just 5 rounds is such a small population that StndDev.P wouldn't be a good predictor of the normal distribution of what you should expect if you loaded and shot significantly more rounds (ie..100). Thus, I agree with you that StndDev.S will better predict what to expect with a particular recipe going forward.

Appreciate your reply as it caused me to think about vs my previous hasty reply

No prob. Though I don't think you will make bad ammo if you use STDEV.P as it's going to be very close.

There's an argument that could be made that 5 rounds made and tested before making say 200 rounds may not have a good chance to be a fair representation of the 200 not made. As you would need to have the ability to randomly choose any 5 rounds of the 200.


However, this logic falls apart. Because you'd still be using those 5 rounds and STDEV.P to make a decision on a recipe to make more ammo. So, you'd still be using those 5 shots to make a decision on future ammo.

 

[PutInOut]

In the end "what difference does it make".

 

[Rob01]

In the end "what difference does it make".

None. Just something to chat about on the internet. Lol

 

[Brijake]

Definitely internet chatter except the guy in the You Tube is basically saying all others basically don't work besides the Garmin. Chatter a lot like some of these forums where guys just hammer each other. Glad this didn't go there…yet

 

[blvette75]

None. Just something to chat about on the internet. Lol

As I am not a competition long range shooter, the only thing I am interested in is how tight are my numbers in my ten shots, once I feel I have a load. I just want to load as consistently as possible. I had held out waiting for something new for a chronograph. I wanted something that was lighter and easier to set up. I am glad I waited. The way things are now, once I optimize will create my ammo per rifle, hopefully will be for multiple years and seasons. Not sure how long the squeeze will be on us, but hope things loosen soon.

 

[Dthomas3523]

In the end "what difference does it make".

Agreed. Zero difference. Unless someone can come up with a scenario I'm unable to imagine.

 

[Rob01]

Definitely internet chatter except the guy in the You Tube is basically saying all others basically don't work besides the Garmin. Chatter a lot like some of these forums where guys just hammer each other. Glad this didn't go there…yet

Yup no need to do that and can't really say that the way we all have done it for years is all of a sudden wrong because a new chrono comes out that does it another way. Both ways give you a good enough number to get a good load worked up.

 

[gregmark24]

I think it does make a difference. If you're shooting 3 rounds per powder development charge, the difference in reported SD is huge with the correct vs Garmin (optimistic) results. If you use a spreadsheet after the fact, or a LabRadar, you'll get correct (less optimistic..) SD's.

 

[Airedale56]

I'm happy for those that have the Garmin. I wish I had waited a little while when I upgraded from a MS to the LR. Such is life in the ever evolving world of electronics. One month after getting a LR the Garmin was introduced.

I get it, same thing happened to me when I bought my first 8-track for my car.
Then it was "Cassette? What the #$&* is a cassette? I just bought an 8-track!"

 

[Buckys]

Shoot, I was hoping my feed was indicating that there was some more practical information about xero experiences to read about.

I think that the simplest answer to the stat question here is by way of example -
say you have made 50 trips to the range with a given rifle/load and shot that setup 20 times each session.

Stdev.p is based on the "population" - the standard deviation around the average velocity for the entire 1,000 rounds you have shot with that setup.

Stdev.s is based on the "sample" - e.g., the standard deviation around the average velocity for the 20 rounds you fired during one session.

https://www.khanacademy.org/math/statistics-probability/summarizing-quantitative-data/variance-standard-deviation-sample/a/population-and-sample-standard-deviation-review

 

[martinakl]

A couple pages ago there was discussion of attaching to your rifle. I've been seeing a few versions of this type of devise:

This is the Area 419 version.

ARCALOCK Arm for Garmin Xero

The Garmin Xero C1 Chronograph is here – and it’s really great. One of the key selling points of the unit is its size, so when we got one we immediately wanted to be able to mount it to the rifle. Our ARCALOCK Arm for the Xero C1 allows you to take advantage of all [...]

www.area419.com

Before anyone forgets to "read the instructions" and pops off... It (It = Area 419's Arm) IS designed to attach to your rifle. Likely not endorsed by Garmin.

"Our ARCALOCK Arm for the Xero C1 allows you to take advantage of all of the unit's versatility, mounted either on the bottom of your rifle or the top."



My Question: Any chance LabRadar can stay in business?

I was an early adopter with the LabRadar. Luckily I was able to use/enjoy it for many years vs. just buying one and the Garmin coming out. It's always been a quirky/finicky thing but I've learned to work with it. That said, I want a Garmin Xero.

 

[jessej]

My Question: Any chance LabRadar can stay in business

To stay in business, they will hafta develop a small lightweight unit comparable to the Garmin, that does more than the Garmin. A proactive marketing strategy would have already had this ready to unveil.

I see them as being more reactive, not good.

 

[Dthomas3523]

I think it does make a difference. If you're shooting 3 rounds per powder development charge, the difference in reported SD is huge with the correct vs Garmin (optimistic) results. If you use a spreadsheet after the fact, or a LabRadar, you'll get correct (less optimistic..) SD's.

As long as you don't try to compare an SD calculated with P and one calculated with S, you'd still come to same conclusion in a comparative analysis.

As far as shooting 3 rounds in general, if you're attempting to make any major decisions, it doesn't matter if you use S or P, your sample size is too small to be reliable no matter which way you go. Even if you use something like a 95% confidence interval, unless you have very low SD in that 3 round sample, you're going to have a very wide range in which your SD likely falls in. And that's before you even take other things into account that make such a small sample size fairly useless for anything worthwhile.

So, unfortunately, on its face, debating the difference in a 3 round sample between S and P is moot, as your sample size (even after extrapolation) is too small to be useable. You just can't get around that.


TLDR: no matter which STDEV calculation you use, you are always being extremely optimistic when you use a 3 round sample for data. It will never be close to "correct." The N-1 denominator for STDEV.S isn't enough to overcome the variance of a 3 round sample.