  For the submillimeter band observations, we have been routinely adopting the
calibration cycle time of 20-30 minutes, which is the same as any typical
centimeter and millimeter band observations. This cycle time, largely corrects
only the instrumental phase fluctuations and there exists residual phase
fluctuations, which are attributed to temporal and spatial atmospheric phase
fluctuations. Hence, the classical calibration cycle needs closer attention for
any future submillimeter band observations. We have therefore obtained
fast-switching test data, cycling between three nearby calibrators, using the
submillimeter array (SMA) with a cycle time of $\sim$90 sec, in order to
understand and optimize the calibration cycle suitably, thereby to achieve the
projected sensitivity, angular resolution and dynamic range for the SMA. Here,
we present the preliminary results from this study.
