In an effort to aid industrial hygienists in interpreting data, a number of specific errors in aerosol sampling and data analysis were presented. These errors included biases arising from inlet and internal instrument losses, limited sensor response, inadequate calibration, coincidence, and oversimplified graphical analysis. Measurement variability was noted to be increased by taking inadequate sample sizes. Through the increased time resolution and direct feedback afforded by direct reading instruments it was possible to improve the understanding of the workplace environment. Recently a great many aerosol sampling techniques have become available and it has been possible to compare one against another only on an absolute basis. It was necessary that inaccuracies in sampling and interpretation be overcome if the comparisons were to be made. The characteristics of the sampling inlet, the transport to the sensor and the sensor itself each affected the aerosol size distribution and, thus, the reported number of mass concentration. The precision of the registered particle size distribution was determined by the particle count in specific size ranges, depending on the weighting chosen. It may be modified further by the type of display and the calibration of the aerosol monitor. The authors note that if the aerosol is transported to the sensor with the same efficiency as in the active mode, then aerosol monitors using passive sampling register the same aerosol size distribution as active ones.