Accuracy vs Precision and Truncation error  

What is a truncation error?, A truncation is caused by dropping the trailing digits of a figure (number); such as by reducing 99.987 to 99.98 or 99.9. Whereas such errors may be harmless in manual computations, they can become serious mistakes in computer calculations involving thousands or millions of mathematical operations, according to that we go to be careful with the numerical approximations we do and take in account several rules for this process.

So, for avoiding this kind of error you need to considerate how to use your data before you start doing calculations, and there are two factors you may consider for this, they are called Accuracy and Precision.


Accurate means "capable of providing a correct reading or measurement." In physical science it means 'correct'. A measurement is accurate if it correctly reflects the size of the thing being measured.
Precise means "exact, as in performance, execution, or amount. "In physical science it means "repeatable, reliable, getting the same measurement each time."
We can never make a perfect measurement. The best we can do is to come as close as possible within the limitations of the measuring instruments.
Let's use a model to demonstrate the difference.
Suppose you are aiming at a target, trying to hit the bull's eye (the center of the target) with each of five darts. Here are some representative pattern of darts in the target.







Now, you can continue studying about truncation error a here is a link about a nice video about that:

http://www.youtube.com/watch?v=NByHuFBkulw