4.12b 
4.12c 
4.13 
  
4.21 
4.22 
  
   
-» lll. 
Is it checked by plotting of & standard stereopair? 
Yes 14 Not answered 2 
No 4T 
Is it checked by other methods? 
Yes 8 Not answered 3 
No 52 
Are there fixed tolerances for accuracy of instruments? 
Yes 52 Partly 
No 7 Not answered 
By how many operators are the instruments run” 
l operator 26 1 or 2 operators 15 
. 2 operators 20 Not answered 2 
For how many hours per day are the instruments exploited? 
5 hours 3 Variable 10 
hours T Not answered 1 
hours 13 
11 hours 4 
12 hours 6 
13 hours 1 
14 hours 8 
15 hours 2 
16 hours 8 
17 hours 1 
18 hours 2