A report expression can take an optional prefix number inside curly brackets to indicate from which reference command the data should be taken.
For example, if you create a label template for a Roundness dimension, and you want to show the measured diameter on the label template, you could use this expression:
={1}MEAS_DIAM()
Notice the {1}. This indicates that the data needs to come from the first reference command (the feature) instead of the command for which the template is being created (the dimension).
If there is more than one reference feature used, the number within the curly braces represents the feature from which PC-DMIS will pull the information. For example, a Distance dimension uses two features to compute the distance. Using {1} would pull information from the first reference feature and {2} would pull it from the second reference feature.