What's the difference between accuracy and precision? - Matt Anticole

譯者: Seke Wei 審譯者: Max Chern

As the story goes, the legendary marksman William Tell

傳說中 有位神射手名叫威廉•泰爾

was forced into a cruel challenge by a corrupt lord.

他受到壞城主脅迫 接受一項殘酷的考驗

William's son was to be executed

威廉的兒子將被處死

unless William could shoot an apple off his head.

除非威廉可以射掉 兒子頭上的蘋果

William succeeded, but let's imagine two variations on the tale.

威廉最後成功了， 但我們來看看另外兩種可能

In the first variation,

第一種可能：

the lord hires a bandit to steal William's trusty crossbow,

城主雇了一名盜賊 偷走威廉信賴的十字弓

so he is forced to borrow an inferior one from a peasant.

於是他被迫向農夫借一把 沒那麼好的弓

However, the borrowed crossbow isn't adjusted perfectly,

可是，那把弓校準沒有非常好

and William finds that his practice shots

他發現那些試射的箭

cluster in a tight spread beneath the bullseye.

全部聚集在靶心下方一塊小區域

Fortunately, he has time to correct for it before it's too late.

幸好他還有時間把弓校準回來，不致於沒救

Variation two:

第二種可能：

William begins to doubt his skills in the long hours before the challenge

威廉在考驗前的緊張等待時刻 開始懷疑自己技術

and his hand develops a tremor.

他的手不禁顫抖起來

His practice shots still cluster around the apple

他練習時射出的箭 仍然聚集在蘋果附近

but in a random pattern.

但是呈現隨機位置

Occasionally, he hits the apple,

偶爾才打中蘋果

but with the wobble, there is no guarantee of a bullseye.

由於會搖晃 所以不能保證一定打中靶心

He must settle his nervous hand

他必須控制發抖的手

and restore the certainty in his aim to save his son.

恢復其命中的必然性 以救回兒子

At the heart of these variations are two terms often used interchangeably:

這兩種可能 正說明了兩種常交互使用的詞

accuracy and precision.

即「準度」和「精度」

The distinction between the two

這兩個詞的區別

is actually critical for many scientific endeavours.

在很多科學實驗是很重要的

Accuracy involves how close you come to the correct result.

「準度」衡量的是 你接近正確結果的程度

Your accuracy improves with tools that are calibrated correctly

準度的提昇需要依賴 正確校準的工具

and that you're well-trained on.

以及你對工具的熟練度

Precision, on the other hand,

另一方面，「精度」則

is how consistently you can get that result using the same method.

衡量你使用相同的方法 可以一致得到相同結果的程度

Your precision improves with more finely incremented tools

精度的提昇需要依賴 越精細的工具

that require less estimation.

以減少不必要的估算

The story of the stolen crossbow was one of precision without accuracy.

故事中偷走弓的情形就是 有精度而無準度的例子

William got the same wrong result each time he fired.

威廉每發箭都得到相同的錯誤結果

The variation with the shaky hand was one of accuracy without precision.

至於另一個手顫抖的情形則是 有準度而無精度的例子

William's bolts clustered around the correct result,

威廉的箭集中在正確結果的周圍

but without certainty of a bullseye for any given shot.

卻沒有任何一發有命中靶心的把握

You can probably get away with low accuracy

日常工作中你可以容忍低準度

or low precision in everyday tasks.

或低精度的結果

But engineers and researchers often require accuracy

但是工程師及研究員 通常要求準度

on microscopic levels with a high certainty of being right every time.

在微觀層面上 每次有高把握一定對

Factories and labs increase precision

工廠及實驗室致力於提昇精度

through better equipment and more detailed procedures.

方法是使用更好的設備及 更仔細的程序

These improvements can be expensive, so managers must decide

這些提昇的花費不貲 所以管理者必須決定

what the acceptable uncertainty for each project is.

每個專案容許多少不確定性

However, investments in precision

可是，精度的投資

can take us beyond what was previously possible,

可以將我們帶到前所未及之處

even as far as Mars.

甚至達到遙遠的火星

It may surprise you that NASA does not know exactly where

你聽了可能感到驚訝 NASA 其實不完全知道

their probes are going to touch down on another planet.

其探測船要在另一顆行星 的什麼位置降落

Predicting where they will land requires extensive calculations

預測其降落位置 需要依據測量結果大量計算

fed by measurements that don't always have a precise answer.

這些計算不一定能產生一個精確答案

How does the Martian atmosphere's density change at different elevations?

火星的大氣密度如何隨著高度變化？

What angle will the probe hit the atmosphere at?

探測船要以什麼角度進入大氣層？

What will be the speed of the probe upon entry?

探測船進入大氣的速度為何？

Computer simulators run thousands of different landing scenarios,

電腦模擬了數千種不同的登陸情節

mixing and matching values for all of the variables.

為所有變數混合及匹配數值

Weighing all the possibilities,

考量過所有可能之後

the computer spits out the potential area of impact

電腦才輸出一塊可能的撞擊區域

in the form of a landing ellipse.

其形狀為一登陸橢圓

In 1976, the landing ellipse for the Mars Viking Lander

1976 年海盜號登陸火星的登陸橢圓為

was 62 x 174 miles, nearly the area of New Jersey.

62 x 174 英哩， 幾乎和新澤西州的面積相當

With such a limitation,

受此限制

NASA had to ignore many interesting but risky landing areas.

NASA 只好忽略許多有趣 但具風險的登陸區域

Since then, new information about the Martian atmosphere,

從那以後 有關火星大氣的新資料

improved spacecraft technology,

提昇了太空船技術

and more powerful computer simulations have drastically reduced uncertainty.

益形強大的電腦模擬 也急遽降低不確定性

In 2012, the landing ellipse for the Curiosity Lander

2012 年好奇號的登陸橢圓就只有

was only 4 miles wide by 12 miles long,

4 英哩寬，12 英哩長

an area more than 200 times smaller than Viking's.

面積小於海盜號登陸橢圓的 1/200

This allowed NASA to target a specific spot in Gale Crater,

NASA 因此可將目標設在 蓋爾坑（Gale Crater）內一處特定位置

a previously un-landable area of high scientific interest.

該區域雖有高科學價值 以前卻無法登陸

While we ultimately strive for accuracy,

在我們最終追求準度的同時

precision reflects our certainty of reliably achieving it.

精度能反應我們可靠達標的把握度

With these two principles in mind,

只要牢記此兩原則

we can shoot for the stars

我們將可立志追星

and be confident of hitting them every time.

且有信心每次命中

翻譯：Seke Wei