Measuring Sig Figs

Question

Hi I'm confused with measuring sig figs. Let's say that the ruler is going up in tenths and our number is exact at 7. Would we still have to include the two zeroes to show that there could be estimation? 

Answer 1

Usually, it is the measuring instrument that determines the number of significant figures.  If your measuring instrument is precise to 3 significant figures, a measurement of 7 should be recorded as 7.00 instead of 7, which means the range of the "true" value is between 6.99 and 7.01.  To 6 significant figures, the measurement should be recorded as 7.00000, meaning the "true" value is between 6.99999 and 7.00001.  Again, it is the instrument that usually determines the number of significant figures.