To measure velocity:

Use the Measure Distance tool to measure the velocity of particle movement.

1. Open an image in the Image window.

2. From the Image window menu, click Tools | Measuring Distances.

3. In the Measure Method option list, select the Standard Two Point method.

4. In the Units options list, select the appropriate unit of measurement.

5. In the Image window, click on the particle that you want to measure.

6. Move the T (time) slider on the Image window to display the particle at a different time point.

7. Click the same particle that you selected at the original time point.  

The distance and velocity of the particle movement are displayed at the bottom of the Measure Distances window.