Labels:book | earth | map | poster | sky OCR: Notes : 1. The values are estimated from many field strength measurements and from known geological for- mations The values apply to the frequency range 500 1500 kc/s. Fffective conductivity va tues vary with fre- quency -. - Conductivity values 4*10 given e.m.u 10 5-10 4-6 *+.* :10-20 5-1b .....* ..... 10 3.6 10 15 LONDON ARE 5.19 ZTS10/2 Fig. Ground conductivity map of the British Isles Effective ET510