432 VALUATION, DEPRECIATION AND THE RATE-BASE
EXPLANATION OF TABLE 31
EXPECTANCY AND REMAINING VALUE
Ari ARTICLES AssuMeED 70 Fam WitEIN A TERM EQUAL TO TWICE
THEIR ORIGINAL EXPECTANCY
(Approximate Values Only)
The expectancy of any article in use, which is still in serviceable
 condition, can be approximated from the following tables,
when the probable life new of other articles of the same class is
known. There is noted in these tables also the approximate
remaining value, although this may also be obtained from the
Amortization or Depreciation Table 33 by entering the same
with the years of expectancy as elsewhere explained. The expectancy
 noted in Table 31 is based on a reasonable assumption
of the rate at which a large number of articles of the same probable
 life would go out of use (see Chapter VI)* and is in fair
accord with the expectancy that would be found if all the articles
were assumed to fail according to the law of probabilities within
a period equal to twice the probable life term. The strict application
 of the law of probability under assumptions, relating
not only to the probable life of any article in question, but also
to the probability of survivals beyond some period, as, for example,
 twice the probable life, would be an unnecessary refinement
 not justified until a vastly greater mass of data than now
available, relating to actual life of individual articles in each
class, has been assembled.
It may be claimed for this table in its present form that it
will afford means of making much closer approximation to the
actual remaining worth of any article than is possible by the
use of the ordinary amortization tables in which age alone is
taken into account and in which no distinction is made between
actual and probable life.
In this table the expectancy and remaining value are noted
for any single article, whose probable life when new is known.
The table has been computed for 4 per cent, 5 per cent, 6 per
cent and 7 per cent interest per annum. For other interest
rates, values may be interpolated.
* Page 104 of “Valuation, Depreciation and the Rate-Base.”