Many hand held GPS receivers deliver time information accurate to within 1 to 40 milliseconds via a serial cable which can be connected to your PC's RS-232 serial or USB port. Many GPS clocks advertise accuracy to within the nanosecond range. PresenTense Time Client supports both hand held GPS
receivers as well as GPS clocks that communicate via the NMEA 0183 protocol.
The benefits of hand held GPS receivers are cost effectiveness and availability - they may be purchased at many outdoor outfitters and office supply stores in every major city as well as online. Depending on the construction of the building in which you intend to operate your time server and GPS
receiver, you might require an external antenna for your GPS to guarantee availability of satellite signals.