451.250 Straight-line method. The assignment of equal segments of the service cost of any item to the benefits to be yielded by the item; a procedure followed in depreciation computations and in the spread of prepaid expenses and bond discount. In practice, a period charge for depreciation is usually substituted for a more exact measurement of benefits yielded because of:

(a) its relative simplicity;

(b) the presence of only minor differences between the two methods;

(c) the impossibility of estimating with any degree of realism the total prospective output of services, as in the case of many types of machinery; or

(d) the absence of any ready determinable unit of service, as in the case of buildings. See amortization; apportionment; deferred charge.