Two different SD's. Which one is correct?

[Hugnot]

I suspect its using decimals that it isn't displaying on screen. With such a tiny sample size and such a tight grouping, rounding up can change the calculation

I suspect its using decimals that it isn't displaying on screen. With such a tiny sample size and such a tight grouping, rounding up can change the calculation.
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Two different data sampling types. I interpreted the data as a population as there were 3 measurements. The other method would be to interpret the data as a sample, but no other data was available.

This resulted in the sum of squares, 4.047 being divided by N or 3 for a population or N-1 for a sample like 2.

My spread sheet shows a sum of squares value of 4.047, and a variance of 2.023 (estimated variance via division of population minus 1)
This agrees with your calculations. Gathering more data will reduce the 1.4 SD that was displayed by the Magneto Speed.

Actual MS data calculations were unknown, but MS treated it as a sample, probably expecting more data. The difference was not caused by "rounding up" it was caused by two different data sampling methods - population (like everything) vs sample (part of everything). Or dividing sum of squares by N-1 (3-1) or N (3).

I enter MS data into my spreadsheet(s) so I can look & compare. The results have adequate accuracy despite whole number data entries. Open Office is much easier to use than On-Line Excel.

So sorry about the pasting remark - I got a history of dealing with data treachery. A good example of which is faking electronic ballot images used for verification. My bad

 

[Hugnot]

OK...I definitely am not going to fake an online calculator result for this thread lol.

You were using population stdev in that online calculator, I was using sample, and since I basically fiddled with the decimals to make a sample stdev come out to about 1.4, a population stdev would have a different result. I'm also pretty sure, but not certain, that the MS uses sample, and the garmin uses population, but I might have the reversed. Regardless, my point that the MS is using numbers with a decimal we can't see stands.
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As for excel, I can't tell which formula you were using, but I came up with similar numbers to the online calculator.
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Data treatment -Population N=3 vs., Sample N-1=2 - reason for 1.16 SD vs. 1.4 SD.

 

[LkeAF]

Data treatment -Population N=3 vs., Sample N-1=2 - reason for 1.16 SD vs. 1.4 SD.

Wow! @Hugnot and @Aloeus, thanks for the deep dive.

 

[Hugnot]

Magneto Speed chrony chip performs math using high precision floating point numbers obtained from magnetic field interruption/time data. Manual entry of fractional values has no effect on precision. See my blast of stuff under Ballistics & other, new post.