ballistics Calculator tab

ripper007 · Member Joined: Mar 05, 2006 Posts: 199 Location: Colorado

on the ballistics Calculator tab at the bottem there are 8 spots to input data

1) Ballistic Coeff
2) Bullet Weight
3) Velocity
4) Std Dev
5) Targ Dist
6) Scope Hight
7) Temp (F)
Cool

Altitude (ft)

I know what every thing means excetp for number 4) Std Dev ?

I looked at the Help tab under Ballistics Calculator Data Fields,
It shows and gives explanations for all except for number 4) Std Dev.

and I do not have a clue to what it means. If some one could please let me know what it is.

Thanks.

Keivn.

DallanC · Site Admin Joined: Jan 18, 2005 Posts: 3572 Location: Utah

en.wikipedia.org/wiki/..._deviation

Quote::

In probability and statistics, the standard deviation of a probability distribution, random variable, or population or multiset of values is a measure of the spread of its values. It is usually denoted with the letter Ïƒ (lower case sigma). It is defined as the square root of the variance.

To understand standard deviation, keep in mind that variance is the average of the squared differences between data points and the mean. Variance is tabulated in units squared. Standard deviation, being the square root of that quantity, therefore measures the spread of data about the mean, measured in the same units as the data.

Said more formally, the standard deviation is the root mean square (RMS) deviation of values from their arithmetic mean.

For example, in the population {4, 8}, the mean is 6 and the deviations from mean are {-2, 2}. Those deviations squared are {4, 4} the average of which (the variance) is 4. Therefore, the standard deviation is 2. In this case 100% of the values in the population are at one standard deviation of the mean.

Basically, it measures the variation in measurements of something. In this case it describes velocity. So you shoot your rifle and you get various velocities, these velocities can be used to compute a standard deviation, or a +/- value from the mean.

I use it to plot low side, high side and median trajectories... if someone wants to.

-DallanC

Bushmaster · Posted: Wed Sep 05, 2007 11:09 am Post subject: Re: ballistics Calculator tab

Whew...Thought there for a moment Dallan wasn't going to put it in layman's terms. Then where would I be...Square one I bet...

ripper007 · Member Joined: Mar 05, 2006 Posts: 199 Location: Colorado

thanks.

so , if I used 3) velocity , do I ned to put any data into 4) Std Dev ?

or would I use them both together, and if so.

lest say, with the wight of a 223 bullet, using max powder grains, that has a out put of 3100 velocity,
what would I put into the Std Dev ?

ya, I am new to this . just learning and want to know what I need to know .

DallanC · Site Admin Joined: Jan 18, 2005 Posts: 3572 Location: Utah

Leave it blank. Its only used by the serious data pushers :). Actually alot of cronographs compute the Std Dev from a shot string. You could then use it to graph out the min, mean and max trajectories together.

Really though just leave it blank Smile

-DallanC