"proportional charges," are called "revenue
expenditure," as distinguished from the capital, or "suspense,"
expenditures. In other words, "revenue" expenditures are those
involved in the daily turnover of the business and resulting in
immediate returns. The inherent difference in character of revenue
and capital expenditures is responsible for most of the difficulties
in the determination of working costs, and most of the discussion
on the subject.

WORKING COSTS.--"Working costs" are a division of expenditure for
some unit,--the foot of opening, ton of ore, a pound of metal,
cubic yard or fathom of material excavated, or some other measure.
The costs per unit are usually deduced for each month and each
year. They are generally determined for each of the different
departments of the mine or special works separately. Further, the
various sorts of expenditure in these departments are likewise
segregated.

In metal mining the ton is the universal unit of distribution for
administrative purpose, although the pound of metal is often used
to indicate final financial results. The object of determination of
"working costs" is fundamentally for comparative purposes. Together
with other technical data, they are the nerves of the administration,
for by comparison of detailed and aggregate results with other mines
and internally in the same mine, over various periods and between
different works, a most valuable check on efficiency is possible.
Further, there is one collateral value in all statistical data not
to be overlooked, which is that the knowledge of its existence
induces in the subordinate staff both solicitude and emulation.

The fact must not be lost sight of, however, that the wide variations
in physical and economic environment are so likely to vitiate
conclusions from comparisons of statistics from two mines or from
two detailed works on the same mine, or even from two different
months on the same work, that the greatest care and discrimination
are demanded in their application. Moreover, the inherent difficulties
in segregating and dividing the accounts which underlie such data,
render it most desirable to offer some warning regarding the limits
to which segregation and division may be carried to advantage.

As working costs are primarily for comparisons, in order that they
may have value for this purpose they must include only such items
of expenditure as will regularly recur. If this limitation were more
gener