For NRR to be 1, Couple protection rate should be

Couple protection rate is an indicator of the prevalence of contraceptive practice in the community CPR is defined as the percent of eligible couples effectively protected against child bih by one or other approved methods of family planning Demographers are of the view that the demographic goal of NRR = 1 can be achieved only if the CPR exceeds 60% Reference : Park&;s textbook of preventive and social medicine, 23rd edition, Page no: 493