The angular scale range which an array configuration covers is determined by the ratio of the maximum and minimum baselines of the configuration. Values of this ratio,
, are different among each array configurations; the value
is used as a representative value at present.
Let SARG = Smallest Angular Resolution Goal and LARG = Largest Angular Resolution Goal. If
, then it is impossible to cover the angular range by a single array configuration. In such a case, the observation is split into more than one SB. The ideal split would be an SB with a desired resolution goal of SARG, then one with a goal of N*SARG, and so on.
However, in reality there are other considerations. Here we bring in the following two conditions:
In terms of hour angle, splitting is only performed when the elevation of the target is low and the resolution required is sufficiently high that one of the "Y" configurations is needed; this combination will not give good uv-coverage. The threshold for elevation is 35 degrees and that for resolution is 0.1 arcsec; consequently observations for which the desired resolution is less than 0.1 arcsec and the elevation lower than 35 degrees are split into two SBs with 0, 12 and 12, 24 as the minimum and maximum allowed hour angles.