What is the units for the Shutter setting in image acquisition toolbox?

Hi, I am using MATLAB to control a "Basler A631f/fc Area Scan FireWire Camera". I set the Shutter to 500.

 videoSrc = imaq.VideoDevice('dcam',1, 'F7_Y16_1392x1040');

 deviceProps = videoSrc.DeviceProperties;

 set(deviceProps, 'Shutter', 500);

What I would like to know is how to convert the 500 into physical time? Is it 500ms or there is any formula for conversion.

Thank you!

[miaochen]

Solved. The unit is 20us.