t3 
No. 2 Deduced reckoning 
2.2.1 Methods: 
Deduced reckoning — using a starting point, heading, drift, true air speed, 
wind vectors, ground speed, time, side sight or next-line offset angle in navigation 
sight. 
2.2.2 Application: 
All areas where maps are inadequate to keep the side lap variations within 
tolerance of + and - 1076 approximately. In the majority of cases, visual check 
points can be used as *updating-fixes" only where they are available. Well re- 
cognized points sighted under the next-line offset angle are used as updating 
fixes. 
2.2.3 Instrumentation: 
Good quality gyrosyn compass 
Maps are not essential. 
Navigation telescope with next-line grid, or special side sight, (drift sight) 
Intervalometer, or: Overlap regulator, controlling the camera. 
No. 3 Ground controlled radio navigation 
2.3.1 Methods: 
Navigation methods based on electronic instruments hooked onto 
ground-based beacons, masters or transponders. 
2.3.2 Applications: 
Primarily for the determination of control: in a large number of countries 
these methods have been extremely useful for the determination of primary 
and/or secondary horizontal control. 
Only in second instance they have been used for survey navigation as such. 
They are not particularly suitable for parallel-line navigation: high level of 
investment, complicated logistics, difficulties in accessibility of ground based 
points, and the necessary ground operations are very much slower than the 
aircraft.