Centre Notifies Legal Metrology Rules to Make Indian Standard Time a Legal Reference

The Government of India has formally notified the Legal Metrology (Indian Standard Time) Rules, 2026, a move aimed at establishing Indian Standard Time (IST) as the country's single, legally recognised and traceable time reference. The rules were issued by the Department of Consumer Affairs under the Ministry of Consumer Affairs, Food and Public Distribution on 27 August 2026 and published in the Official Gazette two days later. They will come into force 180 days from the date of publication.

The framework designates the Legal Metrology Department as the regulatory and enforcement authority, while the CSIR-National Physical Laboratory (CSIR-NPL) — India's National Metrology Institute — will provide the scientific foundation and traceability for IST. The initiative supports the government's broader "One Nation, One Time" vision, ensuring that critical sectors and digital systems operate on a common and reliable time reference.

Accurate and synchronised time is essential for modern digital infrastructure, including telecommunications, financial transactions, power grids, transportation, data centres and government information systems. A common national time reference also strengthens cybersecurity by enabling precise event correlation during cyber incidents. The CERT-In Guidelines on Information Security Practices for Government Entities, 2023, already recommend synchronising ICT systems with standard time sources such as NPL and NIC.

CSIR-NPL maintains India's national atomic time scale using an ensemble of atomic clocks and a primary frequency standard. IST is kept traceable, within a few nanoseconds, to Coordinated Universal Time (UTC) maintained by the International Bureau of Weights and Measures (BIPM). To extend the reach of traceable time, CSIR-NPL, ISRO and the Department of Legal Metrology have jointly established secondary timescales at five Regional Reference Standard Laboratories in Ahmedabad, Bengaluru, Bhubaneswar, Faridabad and Guwahati. These are continuously traceable to IST, creating a distributed national architecture for time dissemination.

CSIR-NPL also provides traceability of IST to ISRO for the NavIC satellite system, enabling satellite-based dissemination of Indian Standard Time. The national timing infrastructure allows IST to be accessed through multiple technologies, including network-based protocols like NTP and PTP, satellite systems such as NavIC, and high-precision optical fibre technologies like White Rabbit, which are being tested.

The distributed architecture reduces dependence on a single dissemination point and provides resilience for meeting growing demand. The notification marks the culmination of sustained efforts to build a traceable, accurate, widely available and secure national timing system, with CSIR-NPL continuing to support NIC, ISRO, RRSLs and other stakeholders in ensuring reliable availability of IST across the country.