  A time transfer link consisting of PTP White Rabbit (PTP-WR) devices can
transfer time with sub-nanosecond accuracy. Originally White Rabbit devices
were calibrated as a set of two devices. Progress in calibration makes
individual absolute calibrated PTP-WR devices possible. This enables exchange
of PTP-WR devices without the need for expensive in-situ end-to-end
calibrations.
  Electrical absolute calibration is the basis of absolute calibration. It
calibrates the time relationship between the internal timestamp and the
external electrical time reference plane. In this paper we examine the
electrical time transfer accuracy when a link is setup using electrical
absolute calibrated PTP-WR devices calibrated by different laboratories.
