Two lab partners measure the same strip of metal. One writes 0.045 m; the other writes 0.0450 m. Same length, but the two records do not claim the same thing.
A measurement's digits do more than state a size. They quietly report how precisely the instrument could read.
Take 0.045 m first. The 4 and the 5 were read off the instrument. The zeros in front were not measured; they only place the decimal point.
Now take 0.0450 m. The extra zero sits at the end, after the decimal point: the instrument really read that place.
So the two records claim different things: 0.045 m claims two measured digits; 0.0450 m claims three.
The digits in a measurement that carry actual measured information are called its significant figures. 0.045 m has two significant figures; 0.0450 m has three.
Two more measurements to count. 7.3 s has two significant figures: both digits were read. 205 m has three: the zero sits between measured digits, so it was read too.
How many significant figures are in the measurement 0.0380 m? Enter the count.
How many significant figures are in the measurement 300.8 s? Enter the count.
How many significant figures are in the measurement 0.007 m? Enter the count.
A digital timer displays 5.600 s. How many significant figures does the reading have? Enter the count.
A caliper reads 0.0102 m. How many significant figures does the reading have? Enter the count.
Which measurement has exactly two significant figures?