This brings us to one thing that uniformly drives students crazy. When anything is measured in the lab, you must keep track of how accurately you can measure it. If you measure your licorice with a ruler, you can pretty easily tell how many centimeters long it is. With a little more effort, you can measure to the nearest tenth of a centimeter. One rule of thumb is that no matter how hard you try, you can only measure to the smallest division on your measuring instrument - in this case 0.05 cm with a ruler marked in tenths of cm, millimeters. This would mean that you are fudging and I will immediately know it if you tell me your licorice is 13.5762 cm long. You cannot measure closer than 13.55 0.05 cm with any accuracy with a standard wooden ruler marked in tenths of cm. It does not mean there is no possible way you can get a measurement with this many significant digits - you do need a better instrument to measure with though. In the following example we have claimed a slightly better accuracy than the rule of thumb given - this is as close as I would want to stretch it.

When you make more than one measurement of a length you are not changing the accuracy of your instrument (smallest division on your ruler) but you can change the precision of your measurement because by repeating the measuring process. When you carefully repeat a measurement several times, you are eliminating the possibility that, for example, you take a poor reading because you forgot to line up the end of the licorice with the 0 on the ruler well. So you are often encouraged to take measurements several times and average the results. Hint - if one measurement seems really different than what you might expect, try measuring it again. This is one of the quickest and least frustrating ways to catch errors in lab, hopefully before you leave for your next class.