10准确度和精度.doc

Unit 10 Accuracy and Precision （准确度和精度）Can you make a measurement thats very precise, but not very accurate?（你能进行一项精度非常高，却不怎么准确的测量吗）Can a number be accurate, but not very precise?（一个量可以正确却不怎么精确吗）Lets find out the difference between these two terms; youll see that precision and accuracy are really two different things.（让我们来找出这两个术语的不同；你将会看到精度和准确度确实是两个不同的概念）A measurement can be precise but inaccurate, as well as accurate but imprecise.（一个测量量可以是精确的但不准确，也可以是准确的但不精确。）For example, if a measurement was made with much care using a highly refined instrument, repeated readings of the same quantity would agree closely and thus precision would exist.（例如，如果一个测量量由仔细的利用高精密的【highly refined】仪器，对一个数重复读数得来，它们将非常一致，精度就存在了）But if the instrument contained one or more undetected, uncorrected systematic errors, the results would be inaccurate.（但是如果仪器含有一个或多个未被发现、未被修正的系统误差，结果将不会准确的）In contrast, it is possible that the mean of several repeated measurements of this same quantity, using a less refined (but calibrated) method, could be closer to the true value and thus this procedure would yield more accurate results even though there was less agreement among the readings.（相反【In contrast】，这个量的几个重复测量值，用的是低精密的（但经过校正的）方法，可以更接近真值，这样，这个过程将产生【yield】更准确的结果，即使【even though】这些读数中【among在之中】的一致性很低）Perhaps the easiest way to illustrate the difference between accuracy and precision is to use the analogy of a marksman, to whom the “truth” represents the bulls eye.（或许最简单的举例说明【illustrate】准确度和精度之间不同方法是，用一个射手的座类比【analogy类比、推理】，“真”就代表了靶心【bulls eye】）Precision: The degree of refinement in the performance of an operation, or the degree of perfection in the instruments and methods used to obtain a result, or an indication of the uniformity or reproducibility of a result.（精度：一项工作【operation】成绩【performance成绩、执行】的精密程度，或者获取结果的仪器和方法的完善【perfection完美、完善】程度，或者一致性【uniformity】程度的指标或结果的重复性【reproducibility重复能力】。）Precision relates to the quality of an operation by which a result is obtained, and is distinguished from accuracy, which relates to the quality of the result.（精度涉及【relates to】获取结果的操作的质量，区别于【distinguished from区别于，disinguished卓越的】准确度涉及结果的质量）Figure 1 shows uniformity achieved by the marksman who is skilled by very small scatter.（图1显示了射手完成的一致性，非常熟练，分散【scatter分散n.】非常小）It illustrates the excellent precision.（举例说明了极好的精度）However, as the shots are far from the center, caused by the bent sight (systematic error), they are completely inaccurate.（然而，由于斜视（系统误差），子弹离中心很远，它们完全不准确）With the knowledge gained by observation of the results, the marksman can apply a systematic adjustment (aim higher and to the left of his intended target, or have his equipment adjusted) to achieve more accurate results in addition to the precision that his methodology and equipment have already attained.（由观察结果得出结论，这个射手可以采用系统的调整（相对于他瞄准的目标，再瞄高一些，向左一些，或者调整他的装备）来获得更准确的结果，来增加【addition增加n.】用他的方法和装备已经获得的精度）【这里的in addition to不是除外的意思，in是介词，that 后面是precision的补语】Such a situation can arise in practice when a piece of EDM equipment produces a set of measurements all agreeing to a few millimeters (high precision) but, due to an operation fault and lack of calibration, the measurements are all incorrect by several meters (low accuracy).（这样的情形也出现在实际当中，当一个EDM装置测出一系列观测值都只相差几mm（高精度），但是由于【due to】操作失误和没有校正，测量值都有几米的偏差（低准确度）【incorrect不准确的adj. by后面表示程度】）Accuracy: The degree of conformity of a final measured value, with respect to the true value as defined by accepted standard (the “truth”).（准确度：相对于【with respect to】被公认的标准（真理）【如三角形的内角和为180，这就是真理】定义的真实值，最终观测值的一致【conformity】程度）Figure 2 shows the shots achieved by the marksman with a wide scatter.（图2显示了射手的子弹分散的很广）It illustrates that the bent sight is now corrected, i.e. the systematic errors are minimized, and the marksman has approached the “truth”, although without great precision.（显示了现在斜视被修正，也就是说，系统误差最小化了，射手接近了“真值”，尽管精度不高）It may be that the marksman will need to change the equipment or methodology used to obtain the result if a greater degree of precision is required, as he has reached the limitations associated with his equipment and methodology.（如果要求更高精度的话，有可能射手需要更换获取结果的装备或方法，当他已经达到装备和方法所能达到的限度时）In Figure 3, the shots are clustered near the center of the target.（在图3中，子弹集中于接近目标的中心）It represents results indicating both accuracy and precision.（它代表了结果显示出【indicate】准确度和精度）In this case, the marksman has probably made one of the systematic adjustments that were indicated by his attainment of precision without accuracy.（这种情况下【In this case】，射手或许做了一个系统调整由他准确度不够的精度达到的【attainment达到n.】程度所显示【indicate】的那样）The degree of precision has not changed greatly, but its conformity with the “truth” has improved over the results obtained in Figure 1. （精度并没有大的改变，但是它与“真值”的一致【conformity】已经超过图1中获得的结果了）The scatter is, of course, due to the unavoidable random errors.（这些离散，当然，应归咎于【due to】不可避免的【unavoidable】随机误差）So from the analysis of precision and accuracy, several important facts should be mentioned as follows.（因此从精度和准确度的分析看出，下列几点重要的事实需要提出：）Scatter is an “indicator of precision”; the wider the scatter of a set of results about the mean, the less reliable they will be compared with results having a small scatter.（离散是一个“精度指标【indicator】”；一系列结果相对于平均值分散的越广，与离散小的结果比【compared with与比】，它们越不可靠【reliable可靠的】）Precision must not be confused with accuracy; the former is a relative grouping without regard to the nearness to the truth, whilst the latter denotes absolute nearness to the truth.（精度不能和准确度相混淆；前者【the former】是不关心是否靠近真值的一个相关群）Precision may be regarded as an index of accuracy only when all sources of error, other than random errors, have been eliminated.（只有当除了【other than除了】随机误差外，所有的误差原因【sources of error】已经被消除【eliminate】的时候，精度可以当作是准确度的指标）An example that explains the difference between precision and accuracy better than any other in surveying has to do with error of closure in traversing.（测量上有一个比其它例子更好解释精度和准确度之间的不同的例子，与导线闭合差【closure闭合差】有关【have to do with与有关】）Many surveyors seem to think that error of closure checks the accuracy of the work.（许多测量者似乎认为闭合差检核的是工作的准确度）Wrong! Error of closure primarily checks the precision, not the accuracy.（不对！闭合差主要检核的是精度，而不是准确度）It checks accuracy only in that it can find blunders. But, since it cannot detect systematic errors in the dist