@staticmethod
def build_summary(val1=None, val2=None, val3=None):
    """Build the Indicator summary using available values."""
    summary = []
    if val1 is not None:
        summary.append(val1)
    if val2 is not None:
        summary.append(val2)
    if val3 is not None:
        summary.append(val3)
    if not summary:
        pass
    return ' : '.join(summary)
