"What is the time?" is probably the most frequently asked question today to which an answer is expected. But if you were to ask this question of 10 different people within a relatively short period of time, there will probably be considerable differences in the answers you get. This may be because some people simply round off the indication on their wrist watches to the nearest 5 minutes or so, or - more likely - because the time indicated on those watches is not correct. The question should thus be: "What is the CORRECT time?"

The National Metrology Laboratory (NML) at the CSIR in Pretoria has the answer. It is charged with the responsibility to maintain and develop the national measuring standards for South Africa, including the national standard for time and frequency. The standard for the latter consists of two Cesium-beam atomic clocks running continuously. The time and frequency of these clocks are being compared on an ongoing basis to atomic clocks all over the world, by making use of the "Global Positioning System" or GPS. The results of the NML’s observations are posted to the International Bureau for Weights and Measures (BIPM - Bureau International des Poids et Mesures) in France. They process the data and the NML receives corrections to the South African time-scale from them.

The BIPM is responsible for maintaining the international time scale called UTC, or Universal Coordinated Time. They receive data from more than sixty laboratories around the world, including ours, and process the data to get an "average" from the contributions of more than one hundred atomic clocks. This "average" is the international time-scale.

The South African Standard Time (SAST) is equal to UTC + 2 hours, and is the one maintained at the CSIR.This time is currently available to users via two services, viz the Telephone Time service and the Network Protocol service. The Telephone Time Service (TTS) enables the user to set the time on his IBM-compatible computer to an accuracy of within one eighteenth of a second. (This limitation is due to the computer hardware and software.) Other equipment can be synchronised to within 1 millisecond, if a communication speed of 300 baud is chosen. This service makes time signals available via the standard phone lines. To make use of the service, a user needs access to a computer with a modem and a copy of the TTS client software. (Copies fo the software can be obtained by completing the attached form and posting or faxing it to the NML.)

The second service is the Network Time Protocol (NTP) service, which can deliver accuracies in the region of 50 milliseconds on the Internet. At present two servers are available to deliver this service. The first is a Stratum 1 machine at tick.nml.csir.co.za, and the second is a Stratum 2 machine at tock.nml.csir.co.za. The Stratum number of a server is equal to the number of hops it is away from an accurately known source of time. A Stratum 1 machine is directly connected to such a source. Our "tick" machine is connected to the Cesium clock. To make use of this service, a user needs access to the Internet and a software package. Software packages for use with NTP is freely available on the Internet, but for the convenience of South African users several of these packages are available on the NML’s website at http://nml.csir.co.za/ntp.html

The NML is supported and sponsored by the Department of Trade and Industry.

Enquiries:

Louis Marais
Time and Frequency Metrology
National Metrology Laboratory
CSIR
PO Box 395,
PRETORIA 0001

Tel: (012) 841 3013
E-mail: elmarais@csir.co.za
Website: http://nml.csir.co.za/