Xero® C1 Pro Chronograph

[Jdaniel344]

Does anyone know how the

Xero® C1 Pro Chronograph​

Calculates standard deviation?
If I try calculating SD by mathematical mean I get different results.

 

[Matches Malone]

Show your work

 

[Jdaniel344]

Here is Garmin Chrony and math for the Chrony numbers. I know .78 isn't much different but why a difference at all?

 

[Conaso]

Rounding?

 

[Jdaniel344]

Could be but I would think it would round up.

 

[Eyesquared]

Garmin shows the population SD and not the sample SD.

 

[Jdaniel344]

Thanks

 

[Matches Malone]

Garmin shows the population SD and not the sample SD.

Is there chronos that use sample SDs? What’s the missing data that makes sample data on a chrono?

 

[Jdaniel344]

IT uses the velocities in the shot string.

 

[Eyesquared]

Is there chronos that use sample SDs? What’s the missing data that makes sample data on a chrono?

I don't have one but my understanding is that the Labradar uses sample SD. The idea being that if I loaded 1000 rounds of ammo and then chronographed 20 rounds of that batch, I would want to predict the behavior of the full 1K and not describe the variation in the 20 rounds I just shot.

I've seen a lot of people doing invalid comparisons between different loadings of ammo using the Garmin because they shot 15 rounds of brand A, 20 rounds of brand B, 10 rounds of brand C, etc. Or they shoot 7 rounds, get a SD of 3fps, and get really excited.

 

[LastShot300]

Garmin shows the population SD and not the sample SD.

Should be the other way around...saying

 

[Jdaniel344]

I think so too.

 

[Changed]

There is already a thread on this. It calculates the actual SD. While many others calculate the projected value for SD.

 

[LastShot300]

There is already a thread on this. It calculates the actual SD. While many others calculate the projected value for SD.

can you point to that thread or expand on what is a "projected" SD ?? never heard of that before. There are Population SD and Sample SD...

 

[Changed]

can you point to that thread or expand on what is a "projected" SD ?? never heard of that before. There are Population SD and Sample SD...

Projected as in a sample taken from a larger data set which is technically a Sample SD. When calculating Sample SD you divide by N-1 where N is the sample size.

So, if memory serves the Garmin uses Population SD, and Magneto Speed Chronos use Sample SD.

Xero® C1 Pro Chronograph

Does anyone know how the Xero® C1 Pro Chronograph Calculates standard deviation? If I try calculating SD by mathematical mean I get different results.

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