Physikalisch-Technische Bundesanstalt

The Physikalisch-Technische Bundesanstalt (PTB) is the National Measurement Institute(NMI) of Germany, which administers the International System of Units( SI). As a state institution, the PTB defines the units and unit systems and is the enforcement institution for the calibration of measuring and testing instruments according to the "Gesetz über das Mess- und Eichwesen" (EichG).

PTB has, among other things, several caesium standards for the exact and highly constant determination of time. It transmits the time signal of the atomic frequency standards via the long-wave transmitter DCF77, via the Internet and via the public telephone networks. For the reconciliation of the worldwide time signals, the PTB signals are compared with other time signals at the Bureau International des Poids et Measures( BIPM) and the international atomic time is calculated from them. In addition, PTB performs measurement and calibration services as well as basic research in the fields of mechanics and acoustics, electricity, heat, optics, production metrology, atomic physics, reactor radiation and in metrology.

PTB is located in Braunschweig, Germany, with one institute in Berlin.