In addition to the amplitude-modulated time signal transmission this information is also transmitted since June 1983 by DCF77 via a phase modulation of the carrier wave with a pseudorandom noise sequence of 512 bits length. Using cross-correlation the reproduced signal at the receiving end can be used to determine the beginning of the second markers much more accurately. The drawback of using phase-modulated time signals lies in the complex instrument grade receiving hardware required for using this time signal reception method. Using this method the Physikalisch-Technische Bundesanstalt (PTB) measured standard deviations of ± 2 to 22 microseconds between UTC (PTB) and UTC (DCF77), depending on the time in the day and season. This was done in Braunschweig located from the transmitter in Mainflingen.