What does it all mean?

[dskinsler83]

I just bought an chrony alpha series chrono and and wandering what all the diff terminology means. Extreme spread? Standard deviation and such what is this thing telling me? I will be using it to check PF and will set it at 10'. Just don't know what all this other stuff means

[CZinSC]

After shooting a string, you should get the following stats in the review:

Hi - High fps of the string

Lo - Low fps of the string

Avg - average fps of the string

ES = extreme spread - This is the difference between your Hi and Lo fps - somewhere around 30 is pretty good, lower is better.

SD = Standard Deviation - This shows how much variation there is from the average. you want a low number, under 10 is Very good, 10-20 is good, if you're getting above 30 consistantly, you may want to check your powder drops

Some one with more experience may be able to throw their two cents in on the ES and SD numbers you are looking for, but basically, you want those numbers to be low.

[Skydiver]

There is a lot of gobblygook on this page (for those like me who barely passed stats) , but to me the most important picture is the graph on the right at top of the page: http://en.wikipedia.org/wiki/Standard_deviation

The smaller the standard deviation, higher the probability that about 68% of your bullets are closer the average velocity... that is the more predictable your rounds are.

Also an alternate way to look at things, if you can set things up so that your average minus 2 standard deviations is above a minimum value would give you a 98% probability that your rounds will be above the minimum.