An improved chart for ionospheric forecasting in the british zone

An improved form of chart for use in ionospheric forecasting is described. In the international 3-zone system of presenting forecasts of radio-wave transmission conditions, the necessity to provide average values over a range of longitudes introduces errors. These errors can be eliminated for the region of the United Kingdom by the use of a British Zone Chart (B.Z.C.), which presents the predictions directly for all 2000 km control points around London. A comparison by various user organizations showed that, over a test period of six months, the standard deviation between the predicted and observed conditions was approximately halved when the B.Z.C. was used.