What is meant by significant figure?
Answers
A significant figure is a figure or a digit that contributes to how accurately something can be measured. Measuring anything is limited by the measuring device you use. For example, a standard meter stick with centimeters as the smallest division can be used to accurately measure to a tenth of the smallest unit, which is a millimeter. Anything smaller than that will be meaningless, since your measuring device only measures to the nearest millimeter. Therefore, if you use this meter stick then measurements like 0.567 meters, or 0.600 meters, are good measurements since they both indicate that you can measure to the nearest millimeter. A measurement like 0.6 meters does not accurately depict that the meter stick can measure to the nearest millimeter. Similarly, a measurement like 0.6123 meters goes beyond the accuracy of the meter stick.
The digits up to the thousandths place then are all significant figures, or sig figs, because together they maximize the accuracy of the measurement being indicated. Given a measuring stick like this, which measures only as small as centimeters, let's consider the process of trying to measure the length of an object. You can only estimate the length of the object to the nearest tenth of a centimeter, or a millimeter; any further isn't possible with the information the ruler is giving us. Let's say the object looks to be about 4.8 centimeters (cm) long, with only two significant figures. The exact length may be different, but with our two significant figures, that's as close as we can get.
But what if the ruler had millimeter markings in addition to centimeters? You could now estimate the length of the object to the nearest tenth of a millimeter. That could give us a measurement like 4.84 cm, with three significant figures. The more significant figures are available to us when measuring, the more exact the measurement will be.