PERCENT STD

Notes on Percent Deviation

Standard deviation is an incomplete representation of measured data behavior. In order to obtain a meaningful number you have to combine Standard Deviation with something else such as the Average Value.

Here is an example of a typical problem, let us assume that you fired two strings with 5 shots each at different velocity ranges. In the example below all values are in Feet/Sec and all results are rounded off to 4 decimal points.  

Shot
Number

String-1
(1020-F/S)

String-2
(120-F/S)

1

1010.00

110.00

2

1015.00

115.00

3

1020.00

120.00

4

1025.00

125.00

5

1030.00

130.00

 

 

 

Average  Value

1020.00

120.00

Standards Deviation

7.9056

7.9056

Percent Standard Deviation

0.7750

6.5880

According to the table above if you relied on Standard Deviation alone, you would be in error by a factor of (6.588/0.775)=8.5, which is a significant amount. 

As you can see, String-1 and String-2 have the same Standard Deviation, yet you know that the shots in String-2 are almost 9 times worst.  In order to solve this problem we have provided Percent Standard Deviation, which performs all the work for you and is defined as

(Standard Deviation)
                                          
(Average Value)
X   100

This is a far Superior performance indicator of your shots. For those who are used to Standard Deviation we still provide it for the compatibility.

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