Within 840 n.mi. the computations were invalid for naviga- 

 tion but of some interest for analysis. Recently the computer 

 program was modified to approximate corrections near 

 transmitters. The modification uses simplified transition 

 criteria and still does not include the effects of the second 

 and higher-order propagation modes. Where applicable, 

 comparisons with observed data have been made with modi- 

 fied corrections. The supplement indicates that the cor- 

 rections may be adequate for some types of navigation even 

 using nearby transmitters. 



TTHi 



40 



20 



00 



80 



60 



40 



20 



00 

 0000 







1200 1600 



2400 



TIME (GMT) 



Figure 6. Bridgefown, Barbados: Criggion-Summit, 10.2-kc/s Omega phase difference 

 (30 Dec 63 to 2 Jan 64). 



21 



