Hi Ed,
You can have both types of error in a single experiment, however you cannot determine statistical (precision or as Ian says uncontrollable) error with one experiment. The manufacturer will usually give some specs on the pipette, 6ul +/- 1ul. In order to verify the specs you would need to perform many pipetting experiments. But even if the manufacturer does not give any specs you still know that the pipette is not perfect and there will be a statistical error, you just do not know what it is. In theory, accuracy or bias could be determined with one experiment. Lets say you thought you had a 6ul pipette but actually it was a 12ul pipette. If you then compare the 'new' pipette against a standard you could tell if it was inaccurate. Of course normally you would repeat this experiment as well because of statistical error. If detected bias can be removed. Systematic error may not be so easily detected. What if the standard is also biased. Adam > One can say it's inaccuracy when it is not estimated and imprecision > when it is. Or one can accept Ian's suggestion and notice that there is > no fundamental difference between things you can control and things you > can potentially control.
