SAT2物理提问A science teacher measures the length of her car to

SAT2物理提问
A science teacher measures the length of her car to be 3.46 m. What is the margin of error in her measurement?


(A) ± 0.001 m
(B) ± 0.005 m
(C) ± 0.01 m
(D) ± 0.05 m
(E) ± 0.06 m


C is not the correct answer. You should have selected D.
Explanation
When reporting a measurement, the last digit is always uncertain, and can be off by as much as one-half the value of the second to last digit. In this case, the science teacher guessed the final 6, meaning that her car could really have a length anywhere between 3.41 m and 3.51 m.
谁能解释一下为什么?谢谢