ence platform on the camera mounts reducing or eliminating the effect of air- 
craft or mount structure flexures on vertical error and on Steadiness. 
5. The Photogrammetric System, being designed with photographic 
applications in mind, will produce a vertical of the required accuracy which is 
also steady. Previous designs, especially navigation systems, have been solely 
concerned with the reduction of the magnitude of the errors. Even motions within 
the limits of these small errors can produce excessive unsteadiness for photo- 
graphy. For modern cameras only a few seconds of arc motion during an ex- 
posure period is permitted. 'This can be realized only by great attention to the 
design to reduce the error rates as well as the error.