For an introduction to flow control technology, see this document on the World Wide Web:
http://www.racal.com/dcom/modem.tutorial.html
For modems (and modem cables, if you have an external modem) which properly support flow control, Hardware flow control can reduce the chance of a communication error.
For more information about Time Division/Hardware flow control, see this document on the MFM web:
http://www.mfm.com/support/timediv.html
You should first select Hardware flow control. If you have any problems with flow control, you'll probably notice them first while you are viewing photos. If you experience communication errors, photo lockup, smeared photos, diagonal stripes (sun rays), or no color data, you should try Time Division/Hardware flow control as well as making sure you selected the correct modem.