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technical and demand conditions prevailing at that point. But 
owing to the simultaneous change of the two component struc- 
tures (physical quantities and relative prices), their comparisons 
through time entail the so-called « index-number problem ». 
The difficulties arising from this problem may be negligible 
when comparisons refer to short periods of time, but they in- 
crease more and more as the time elapsing between the aggre- 
sate magnitudes to be compared becomes longer and longer. 
8. Short-run flexibilitic 
Before closing the chapter, it may be useful to hint brief, 
at short-run possibilities of adjustments. If displaced from po- 
sitions of long-run equilibrium, the system possesses in the 
short run, some important possibilities of flexible adiustments, 
owing to the parameters «, 3 and T. 
The values of x, 3, T which enter the model represent the 
long-run normal values of these parameters, which may be 
constant or showing mild trends in time. But in the short-run 
these parameters can be easily and widely influenced, thereby 
affecting the size of the stocks that the svstem can utilize. This 
means that productive capacities and labour never represent 
absolutely rigid concepts, at least in the same way as the 
physical equipment and the population existing at any certain 
lime do. Between these latter physical concepts and those parts 
of them which are relevant to the productive process, the men- 
‘ioned parameters provide a sort of flexible cushion. Tempo: 
rary variations of 3 and T mean temporary increases in the 
productive capacities of existing physical plants by utilizing 
them more intensively or by keeping in operation some mach- 
ines which were due to be scrapped. Similarly, variations of {3 
and « mean increases of working-hours out of a given po- 
pulation. obtained by lengthening the working week or by 
‘10] Pasinetti - pag. 93