= 
  
    
cision. However, representative fractions somewhere between 1:15,000 and 1:20,000, 
could not be mapped directly at a scale of 1:5,000 by means of the A6. 
An attempt to improve the A 6 along with the A5, and to develop simultaneously with 
the A7 Autograph a new A8 plotting instrument was in order as meeting the requi- 
rements of the day better in allowing a greater magnification between picture and map. 
First it was established by close comparisons that the evaluating precision at the 
higher magnifications is greater where the floating mark is moved by the handwheels 
than where it is moved direct, free hand, as in the A6, a method which is most con- 
venient otherwise. Accordingly, this was abandoned in favor of handwheel operation. 
This offered the possibility of connecting a drafting table to the machine, with a simple 
transmiss on in between. 
In other respects, the basic principle of the A6 has been changed very little so that its 
standard parts and assemblies could be used. In its mechanical design, however, the 
A8 shows certain essential changes. 
The standard linkage mounting was kept, but the rods are now below the pictures and 
illumination is supplied from above by means of a mirror. This results in a simpler 
construction of the linkage, a reduction in the amount of heat delivered to the picture 
carriage and a shorter light path for the viewing optics. Furthermore, the same picture 
carriage as for the A 7 can be used and, if need be, even the same compensation plate 
holders. 
The articulation of the rods is carried by a column along the Z-axis, and guided by a 
carriage movable along the X-axis. Altitude readings are taken in meters or English 
feet on interchangeable glass scales, the divisions of which are projected with consider- 
able magnification on a ground glass plate. The X carriage is free to move on the Y 
carriage, which, in turn, slides on a strong base plate. X and Y spindles carry drum 
counters for the determination of the observing distance. This is adjustable from 98 to 
217 mm, as in the case of the A 7, the largest picture size also being 23 x 23 em (9-06"). 
The A8, thus, is as universally adaptable as the A 7, with regard to cameras. 
Concerning the mechanical design, it remains to be stressed that a double yoke is 
bolted to the base plate. The double yoke carries two bearing shells, in which the 
symmetrically built main frame, with its base group and eyepiece sleeve, is mounted. 
The latter carries two cradles which can be tilted in suitably mounted roller bearings 
(^ V" arranged) about the -axis, and which carry the camera carriers. These can be 
tilted about their p-axes. The flight base, too, can be tilted together with the main 
frame. The areas of orientation are the same as in the A 6. 
The base is adjusted symmetrically with respect to the center of the instrument, by 
means of a crank. 
The symmetrical arrangement of the elements with respect to the spatial model permits 
a very quick absolute orientation, without any calculation in most practical cases. 
Either a small drafting table, with a drawing surface 80x80 cm (31:5") or the A7 
drafting table with a drawing surface 1005100 (39-37") and coordinate recording 
mechanisms can be attached to the A8. 
The transmission gear between the machine scale and drafting table permits 13 
different transmission ratios from 4:1 to 1:4. 
The simple mechanical construction lends itself to rapid assembly and disassembly. 
The adjustment, too, is very simple. The A8, therefore, can be used as a movable 
instrument as well.