Users of the GLAs DGPS system need to be aware, however, that :

a. the system will be operating on a trial basis for a period while validation and other checks are undertaken;

b. DGPS relies inherently on GPS, the operation and characteristics of which are outside the control of the GLAs and their respective Governments;

c. all radio navigation systems are susceptible to interference (including jamming) and environmental effects, which can adversely affect their reliability;

d. various DGPS receiver types are available, some of which may not
- have the facility to provide transformations from WGS84 Datum to the regional datum of the chart
- provide appropriate or timely integrity warnings in respect of the system.

The GLAs strongly advise that no single aid to navigation system should be used in isolation and that DGPS users should use all alternative means available to cross-check the information received. Users should also ensure that they have a receiver which gives sufficient warning of the complete loss of the DGPS signal and reversion to GPS.