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 
String1 
String2 
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, String1 and String2
have the same Standard Deviation, yet
you know that the shots in String2
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) 
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.