Garmin Xero - update

[Aloeus]

Has anyone else noticed that the Garmin SD's report lower than LRadar? Two of us shot with his (Garmin) and mine (LR) using both on one rifle and then both on the other rifle. Velocities were very close, but Garmin SD's were 10-15% reported lower than LRadar. When we later entered the velocities from both into an Excel spreadsheet, the LRadar SD's were correct and the Garmin's were too low

I think the Garmin uses the population formula where most everything else uses sample. This will mean the Garmin's SD value will be lower, with less samples used the greater the difference. Why does garmin use population? I'm not sure, its been a long while since the stats class I took, but it seems to me sample SD would be more accurate. Either way I don't see it being a deal breaker, just something to keep in mind.

 

[orkan]

Lots of folks assume that the LR is the reference. Says who?

Says labradar. I guarantee it...

Because when I called them about a velocity discrepancy in the first unit I got from them, compared to my magnetospeed... that's exactly what they said. lol

Knowing what I know now, I'd trust a velocity estimate from a crack head over that of my lab radar, either of them. (I have 2, because that's how many I felt I need to have in order to trust the result) Ok, maybe they aren't that bad... but I really don't like them.

Still today, if I really need to know what the velocity actually is, out comes the Magnetospeed.

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[gregmark24]

I think the Garmin uses the population formula where most everything else uses sample. This will mean the Garmin's SD value will be lower, with less samples used the greater the difference. Why does garmin use population? I'm not sure, its been a long while since the stats class I took, but it seems to me sample SD would be more accurate. Either way I don't see it being a deal breaker, just something to keep in mind.
View attachment 521630

Exactly. A sample size of three is not a "population", but a "sample".

 

[Earnhardt]

Interesting you say that. How do we know, with absolute certainty, which one is correct? Point is we don't. Lots of folks assume that the LR is the reference. Says who? The differences are so small it may not matter much. It certainly won't make that much difference to me. Your milage may vary.

Winner, winner...chicken dinner...

 

[C-130 Dude]

Says labradar. I guarantee it...

Because when I called them about a velocity discrepancy in the first unit I got from them, compared to my magnetospeed... that's exactly what they said. lol

Knowing what I know now, I'd trust a velocity estimate from a crack head over that of my lab radar, either of them. (I have 2, because that's how many I felt I need to have in order to trust the result) Ok, maybe they aren't that bad... but I really don't like them.

Still today, if I really need to know what the velocity actually is, out comes the Magnetospeed.

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I understand you point here. But every manufacturer will say theirs is the best thing since sliced bread.

 

[Justice1327]

Ok, I put the Garmin at 170yds and pointed it at the 200yd target, had it on the same plane as the target and fired 10 shots. Guess what…NOTHING! Didn't take a reading. Open for suggestions or an answer as to why it wont work. Garmin only told me that is not how it is designed to work, but wouldn't tell me more.

 

[cowboy]

Ok, I put the Garmin at 170yds and pointed it at the 200yd target, had it on the same plane as the target and fired 10 shots. Guess what…NOTHING! Didn't take a reading. Open for suggestions or an answer as to why it wont work. Garmin only told me that is not how it is designed to work, but wouldn't tell me more.

I assume the Garmin was in the 5"-15" path of the bullet??

 

[gregmark24]

Interesting you say that. How do we know, with absolute certainty, which one is correct? Point is we don't. Lots of folks assume that the LR is the reference. Says who? The differences are so small it may not matter much. It certainly won't make that much difference to me. Your milage may vary.

You know which one is correct when you compare with Excel. Excel is everywhere, and is often used by statisticians. It is the reference for Standard Deviation.

 

[gregmark24]

Ok. Here you go. For a point of reference, look at Load #2. Take the three velocities 2632.1, 2609.9 and 2628.9. Excel STDEV says 12.0, and Excel STDEVP comes up with 9.8. Garmin has 9.3. I'd say that Garmin calculates SD wrong. This is from the session with my buddy, and he got one of the early Garmin units. Perhaps it has been fixed by now. I'd be interested if any of you have three shot strings that give you the correct SD; or not. When I entered in the values from my LabRadar, my Excel SD results were EXACTLY the same results as the LabRadar.

 

[C-130 Dude]

You know which one is correct when you compare with Excel. Excel is everywhere, and is often used by statisticians. It is the reference for Standard Deviation.

Not exactly true-sort of. I have been using Multical, VisiCalc, and Excel since they were developed in the late 70's and early 80's. We found that all of them (and any other program similar) are only able to run the data "provided". As it's said in the industry, "garbage in-garbage out". If the raw data from each is skewed, bad results will be calculated no matter how they are considered. The issue here is more basic. And it may very well be in the data generation itself by each chrono. The only way this ongoing debate will be judged is to use some sort of industry reference standard measurement chronograph. And measure the contenders against it, not each other. Only then can this be settled. I would imagine these are available, but at what cost. I'm sure all the chrono manufacturers do their utmost to ensure their product does its best. But if it comes down to 100% perfection, I don't think there is a winner. If there was, we would have heard about it.

 

[coyotewillie]

Ok, I put the Garmin at 170yds and pointed it at the 200yd target, had it on the same plane as the target and fired 10 shots. Guess what…NOTHING! Didn't take a reading. Open for suggestions or an answer as to why it wont work. Garmin only told me that is not how it is designed to work, but wouldn't tell me more.

Once again, I have to ask...who puts their chrono out next to the target? I've NEVER heard of anyone doing that! So do you put your Magnetospeed/Labradar out next to the target? I'd be scared to death a wind gust would shove the bullet into the chrono.

 

[gregmark24]

There's only two ways to calculate SD. One with a sample N-1 in the denominator, and one with the full population, N in the denominator. My hand calculations agree with Excel's and LabRadar's results. My 2c worth is that this Garmin, or at least the early units are too optimistic on SD.

 

[C-130 Dude]

There's only two ways to calculate SD. One with a sample N-1 in the denominator, and one with the full population, N in the denominator. My hand calculations agree with Excel's and LabRadar's results. My 2c worth is that this Garmin, or at least the early units are too optimistic on SD.

Math doesn't lie. It's the data supplied against the standard that is the problem. More to the point, what standard? I've never heard of any of these chronos being measured against an industry standard measurement chrono.

Optimistic? Are you saying that the Garmin is calculating results to small (lower) or large (higher) numbers?

 

[gregmark24]

The Garmin is calculating SD way too low, ie optimistic. 9.3 vs 12.0. I believe the actual displayed velocities are accurate, and don't know if my friend's early-made Garmin is calculating SD wrong from three velocities, or if all Garmin's are. I'm hoping other folks with both Garmin chrons and Excel (or other apps to calculate sample SD's) can verify the results agree or not