“舍”(round down)、“入”(round up)大家都知了, 不赘。“五留双”之英文是round-to-even, 目的是为了减少修约误差(round-off error, or rounding error), 以下面四个数字修约至小数後一位(round to one decimal place)为例:
12.15
12.25
12.35
12.45 (总数49.2)
若是“四舍五入”的话, 得
12.2
12.3
12.4
12.5 (总数49.4) 进位会太多
若是“四舍六入五留双”的话, 得
12.2
12.2
12.4
12.4 (总数49.2, the round-off error could be minimized)
In determining compliance with a numerical limit, the calculated result of a test or assay is first rounded to the number of significant figures stated, unless otherwise prescribed. The last figure is increased by 1 when the part rejected is equal to or exceeds one half-unit(五入), whereas it is not modified when the part rejected is less than a half-unit. ]
= = = = = =
我们试验所中多数测试都用四舍五入, 一来分别很小, 二来“五留双”不方便操作( There is no built-in function for“round-to-even” in Excel). 但仲裁测试中, 如果是marginal case, 则要小心复核, 有规范跟规范, 规范没指定修约方法就跟相关的国家标准(BS, ASTM etc.)
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