The calculation of linear dimension and image area using a digitising tablet and personal computer.

An inexpensive image-area and perimeter-length measurement system consisting of a personal computer and digital graphics tablet is described. A study to assess the efficacy of the system has shown that accuracy and reproducibility of area measurement increase with increasing size of cross-sectional area. The system generally underestimated all derived areas by less than 2%. Reproducibility of measurement, as defined by the coefficient of variation, was typically less than 2%; the greatest inaccuracies and variability occurring with shapes of smaller cross-sectional area. The system seems to be the least accurate when it measures shapes with rectangular symmetry. Neither direction of digitisation nor operator skill seemed to influence the measurement accuracy of the system.