| 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 |
String-1 |
String-2 |
|
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) |
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.