Error Bars

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Suppose the position of an object is 1.26 +/- 0.4 m at time 4.2 +/- 0.2 s. Suppose you want to graph this data point. How do you do it?

Of course we could simply graph the point (1.26 m, 4.2 s), which represents our best estimate for the point, but actually what we have is not a point! The position could reasonably be anywhere between 1.22 m and 1.30 m, and the time could reasonably be anywhere between 4.0 s and 4.4 s. Your "data point" is actually a "data rectangle"!

error bar animationInstead of indicating the precision of a data point using a rectangle, it is common practice to use "error bars" to indicate precision. (I suppose coloring in all those big rectangles doesn't seem like a good use of time to physicists, and it would certainly get confusing with closely-packed points!) Error bars are simple to draw, and most software packages designed for scientific graphing, such as Graphical AnalysisTM and Science WorkshopTM, will do them for you quite easily.

last update July 14, 2000 by JL Stanbrough