Human precision of operating a digitizing board: implications for electrocardiogram measurements.

To investigate the precision achieved by human measurement on a digitizing board, 100 healthy volunteers (46 women, mean age 36 +/- 12 years) were asked to measure 15 times on artificial pattern composed of 15 points. A high precision digitizing board (programmed to the technical accuracy of +/- 50 microns) was used, and mean and maximum errors in measuring the same distance repeatedly and relocalizing the same point repeatedly were obtained for each volunteer. A median mean and maximum error of 0.2 mm and 1.0 mm were found for repeated distance measurement. When simulating QT dispersion measurement (measuring the same distance 12 times), median value of 20 ms was obtained for ECGs of 25 mm/s paper speed. The study concludes that human precision of operating a digitizing board is rather poor. A recommendation is given to use either a computer screen for manual measurement of ECGs or to provide an operator of the digitizing board with an immediate feedback of the precision and measurement stability achieved so that erroneous measurement can be actively rejected.