1) RMS expected in given time. In this mode you can enter your desired integration time in minutes and the central frequency of your expected line in GHz to determine the sensitivity in the selected units (mK or mJy).
2) Time required for target RMS. In this mode you can enter your desired sensitivity in mK or mJy, and the central frequency of your expected line in GHz to determine the integration time required to perform the requested observation.
Help on this calculator