That is not to say that the exercise of the power conferred by s. 21A is free from difficulty. The reasons expressed in Rogers and Evans display the difficulties involved. As the system of earning remissions for good conduct is regarded - whether rightly or wrongly, I do not know - as a valuable incentive to good order in the prisons, the sentencing judge may need to foretell the prisoner's conduct to some extent and to form some view about the efficacy of the remission system in rehabilitating prisoners and securing good order in prisons. There is a further difficulty - perhaps more apparent than real - arising from the text of s. 21 (discretion of the court to decline to specify a non-parole period) and s. 21A (discretion of the court to exclude reduction by remissions). The grounds on which an order under s. 21A may be made correspond with the specific grounds on which the court may decline to specify a non-parole period under s. 21, though s. 21 includes a non-specific ground - "any other reason which the court considers sufficient". If the court does not decline to specify a non-parole period "by reason of the nature of the offence or the antecedent character of the person convicted", is there any reason why the court should, on one or other of those grounds, refuse the prisoner entitlement to remissions? The partial correspondence of the grounds prescribed by s. 21 and s. 21A raises that problem but also points to its solution. The armoury of the sentencing judge has been enlarged and, where one of the specific grounds prescribed by ss. 21 and 21A appears, he may tailor his sentence to the exigencies of the particular case by exercising his powers under either section or under both sections or by refraining from exercising those powers. The options open to the sentencing judge now range from the imposition of a head sentence without specifying a non-parole period and without entitlement to remissions to the imposition of a head sentence with a specified non-parole period, both periods being subject to the prisoner's entitlement to remissions. As that is the legal effect of the Act in its present form, sentencing judges will encounter difficulty in its administration because of the considerations to which Street C.J. and Hunt J. referred. But that difficulty does not relieve the court from the duty of exercising the power conferred by s. 21A. It will not be surprising if different judicial minds place differing importance on the desirability of leaving the remission system intact. The discretion is at large and there is no a priori reason to assume any bias in its exercise: in some cases the advantages of the remission system may prevail; in other cases, it will be appropriate to ensure that a fixed non-parole period shall be given the effect which the sentence purportedly intends. And the length of a non-parole period may depend on whether the period may or may not be reduced by remissions. Therefore, the principle stated in Power [21] is necessarily qualified by the operation of s. 21A. When one of the grounds prescribed in s. 21A appears and a judicial discretion to disallow remission entitlements is enlivened, a sentencing judge who proposes to specify a non-parole period must now consider whether the minimum punishment by way of confinement which the crime calls for should be expressed as a period which is fixed and irreducible, or as a period liable to reduction by remissions.