358 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
If ©, is put equal to 0.69, the average amortisation period 
for investment, ©,, is 
(334-31) © Je | # 
, = © De EE 
0. df 
© - (1-21), 
4-56 - 0.684 x 0.69 
0.316 
whence 
O,=12.0 
T'his value must be compared with the values shown in tables 8, 
9 and I1 of 0.56, 8.15, and 12.18. 
9) Taking hypothesis (H) in conjunction with table o, 
the average amortisation period of the primary inputs cor- 
responding to investment I is 8.15, whereas it is 12.9 in the 
calculation immediately above. At first sight, these figures 
appear to be rather low for the entire range of equipment and 
structure (1). 
() At all events, it should be borne in mind that, independently of the 
basic assumbtions of the exbonential model, we should have (condition 
(23-12) 
Yc 
ec 
= I—vyc (i—p) 
2 relation which holds for primary inputs taken as a whole whatever the 
function ¢(6). 
This condition depends onlv on the assumption of invariance over time 
11] Allais - pag. 162