Binding effect of departmental circulars: they constrain the Revenue from acting contrary and do not bind courts or assessees. Circulars and departmental instructions function as contemporaneous expositio and guide tax administration, but they cannot override the statute. While not binding on courts or taxpayers, a circular in operation is binding on the Revenue, preventing the department from taking a contrary stance; administrative actions contrary to such circulars, including show cause notices or demands, are open to challenge as invalid.