Love this discussion. We're frequently asked to calibrate pipettes to manufacturer's specs by clients who like the idea of it... but perhaps don't really need it. As mentioned a few times here, manufacturer's tolerances frequently result in a great deal more as-found failures... which means as-found failure investigations, which means money and time spent. You'd want to be sure that it wasn't unnecessarily.
We always advise clients, as has been advised here, to determine what tolerances are required given the type of work you are doing. Can you tolerate 3% accuracy and/or precision? Or do you need 1% or less? (Further, what is the volume range of the instrument that you're working with? What's reasonable given the volume range?)
ISO 8655 is interesting for a number of reasons. Someone else already pointed out that the manufacturers like to tout the best inaccuracy and imprecision because it gives them a competitive advantage when selling their instruments. But let's take a look at it. (Quoting from my company's presentation on pipetting technique)
[FONT="]ISO 8655 stipulates that pipettes must be adjusted to deliver correctly at 101 [/FONT][FONT="]kPa[/FONT][FONT="] barometric pressure (sea level), 50% relative humidity, and [/FONT][FONT="]20°C[/FONT]
[FONT="]Furthermore, the related part six of this standard (ISO 8655-6) requires that equipment (pipette and tips) be brought into thermal equilibrium with the sample solutions by waiting at least two hours prior to performing calibration testing.
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These tightly specified environmental conditions can be met in carefully designed and controlled calibration laboratories. Each manufacturer must build and maintain a laboratory at sea level that will meet these environmental conditions, and all conformity testing must occur in these laboratories.
Why? Because temperature, humidity and barometric pressure all have an effect on volume.
By ensuring that each manufacturer is testing its instruments in identical environments, we are allowed to compare “apples to apples” when shopping for pipettes for our laboratories.
Manufacturers publish and market the accuracy and precision of the pipettes they sell and use that information to position themselves favorably in the market. In other words, manufacturers compete with each other to produce the most accurate and most precise instruments.
ISO 8655 requirements ensure that performance claims are based upon instrument performance in identical environments.
Because the vast majority of scientists use pipettes in laboratories with environmental conditions that are less tightly controlled than the environment in which manufacturers test their pipettes, pipettes may behave less reliably or differently in your lab than their published capabilities.
As someone else pointed out, not even manufacturers will use the 8655 tolerances when calibrating pipettes after the sale... they are so hard to meet, especially outside of the tightly controlled environment described above.
So the question remains, what are you using your pipettes for?
I would post a link to a white paper here on the topic of tolerances that might further this discussion, but need two more posts before I am allowed. Maybe later.