59

a = 90

FIGURE 38. - Standard Cross-Section Method (Parallel Sections). A, Common wedge formula;

B, cone (pyramid) formula; C, frustum of a cone formula.

In practice, the frustum formula is avoided because of complications

involved in computing square roots and in certain cases it is less accurate

than the prism formula. Let us consider a block of a regular prism (volume

of which is V = S x L) and divide it into two auxiliary prisms in the form of

truncated wedges with areas S4 and SB equal to 0.9S and areas S3 and Ss equal

to 0.1S (fig. 39) (30).

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