How can I calculate blink rate from eye-tracking data in D-Lab3?

If you export the raw data (File > Export > Data): you will be able to output the pupil coordinates, size, height, width, etc. for each frame of your data recording/task in a text file. In this export, you will see that the pupil values are 0 when there is no pupil detected (i.e. blink) – this allows you to determine whether a frame contained a blink or not.