ALMA's default calibration strategy will provide some level of positional accuracy for e.g. a point source in an image. If better than the default accuracy is required, this should be indicated by selecting enhanced positional accuracy. Although ALMA does not yet have a commissioned astrometry mode, this information will be used to determine those projects that might benefit from a custom calibration strategy e.g. the use of additional phase calibrators, or from observing in better than the default weather conditions.
If enhanced accuracy it selected then it is necessary to complete a special section in the Technical Justification node.
Requesting enhanced positional accuracy is not allowed for Large Programs, VLBI or Stand-alone ACA.