Lately it seems that I've been answering questions about how to determine the dial frequency when using frequency shift modes w/ a TNC (rtty, amtor, pactor, etc.) Here is a good website that has a calculator to do it for you and a brief explanation

http://kn4gc.us/dialcalculator.html

Here's the math, if you want to do it yourself:

For LSB, take the starting frequency + TNC Center frequency.

For USB, take starting frequency - TNC center frequency.

Some TNCs have fixed center frequencies that you can't change. Some (most) don't have a "center frequency" value, but have a "mark" and "space" frequency value, in Hz. In this case you must calculate the center frequency. This is accomplished as: (space + mark)/2.

Hope this helps someone.