Dave is right. Unless you are very careful with camera setup and view calibration using the measurement tool (in Dartfish or any other 2D analysis tool) at all is not a good idea if you’re interested in accurate data. Having said that, the information you do get may be useful for intra-session /meet capture as long as the camera is not moved and the above criteria are met. Even in this case though the measurement error would be far greater than 1/1000. You could measure it but you wouldn’t be able to say with any reliability that what you measured was the actual distance or was just a product of the measurement error. If you wanted to ignore the above warnings, I suppose you could just change the scalling factor to different units. So for example, if you had preset points for calibration scaling set 1m apart, you could enter a scaling factor of 100 (cm) or 1000 (mm) instead of 1 (m) to get more information. This however would only give you a greater quantity of information……..not more accurate information.