Precision, on the other hand, is concerned with the closeness of two or more measurements to each other, rather than to a standard value. It is measured by the correlation (or coefficient) of variance (%CV). The %CV is calculated by calculating the standard deviation of a sample, then dividing this by the mean and then multiplying by 100. It is possible for a group of values to be precise without being accurate. The pipette could be consistently inaccurate- but this inaccuracy could be very precise, for example if a pipette read consistently low.
There are a number of different ways of carrying out pipette checks but the easiest way is the gravimetric method involving water. A number of weighings of water are made onto an analytical balance of water at the uppermost allowable setting of the pipette and a number at the lowest allowable settings as defined by the manufacturer. A conversion factor then changes weight to volume taking into account the atmospheric pressure and temperature of the water, both of which affects the density (and therefore the weight) of the water for a given volume. Calculations can then be carried out to determine the accuracy and precision.
Usage
The user simply makes ten measurements at the bottom end of the range of the pipette and ten at the top end of the range of the pipette then enters them into the program (after making a note of the temperature and pressure). The program calculates the accuracy and precision according to pre-set values or several international standards. The inevitable screen shots can be seen here.
A single user licence is £50 sterling, $70, or 70 euros. A multi-user licence is £200. Under certain circumstances (such as to users in developing countries) the program is free, please contact the author for details.
Does pipettechecker track the performance of pipettes?
No, if you want software that does that then you want one of the more expensive, larger and more complicated rivals.
Contact the author see bootom of the page
Demo version!
Or better still, download a fully working demo from here.
Note; this is limited to 20 uses or 90 days (whichever comes first)-for further details are in this file. Extract
the files to a folder (keeping the help files recursed). If you download
the demo and like it you should pay softwrap.
You pay them via credit card following the instructions in the demo
version. If you wish to pay by other means or for multiuser versions contact
me as above directly. My computer is of course virus checked on a regular
basis using the latest up to date antiviral software, but you download
at your own risk.....
News-more low cost scientific soutions are here and an update for pipettechecker see news for more details.......
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