REQUISITE VARIETY 



11/14 



would deal with twenty subjects that are (for exposure and distance) 

 distinct, then his camera must obviously be capable of at least twenty 

 distinct settings if all the negatives are to be brought to a uniform 

 density and sharpness. Where the law, in its quantitative form, 

 develops its power is when we come to consider the system in which 

 these matters are not so obvious, and particularly when it is very 

 large. Thus, by how much can a dictator control a country? It 

 is commonly said that Hitler's control over Germany was total. 

 So far as his power of regulation (in the sense of S.10/6) was con- 

 cerned, the law says that his control amounted to just 1 man-power, 

 and no more. (Whether this statement is true must be tested by the 

 future; its chief virtue now is that it is exact and uncompromising.) 

 Thus the law, though trite in the simple cases, can give real guidance 

 in those cases that are much too complex to be handled by unaided 

 intuition. 



CONTROL 



11/14. The formulations given in this chapter have already 

 suggested that regulation and control are intimately related. Thus, 

 in S.l 1/3, Table 11/3/1 enables JR not only to achieve a as outcome in 

 spite of all D's variations; but equally to achieve 6 or c at will. 



We can look at the situation in another way. Suppose the decision 

 of what outcome is to be the target is made by some controller, C, 

 whom R must obey. C's decision will affect i?'s choice of a, ^ or 

 y ; so the diagram of immediate effects is 



D 



R 



Thus the whole represents a system with two independent inputs, 

 C and D. 



Suppose now that i? is a perfect regulator. If C sets a as the 

 target, then (through i?'s agency) E will take the value a, whatever 

 value D may take. Similarly, if C sets b as target, b will appear as 

 outcome whatever value D may take. And so on. And if C sets a 

 particular sequence — a, b, a, c, c, a, say — as sequential or compound 

 target, then that sequence will be produced, regardless of jD's values 

 during the sequence. (It is assumed for convenience that the 

 components move in step.) Thus the fact that R is a perfect 



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