I was reading in my chemistry book about significant numbers. Also about measured and exact numbers. From what I understand, a measured quantity can be different than an exact number. The book said when comparing something, like 1 lb = 16 oz, it is an exact number because the two are the same (or exact). If I have 5 apples, it is an exact number. But it says if I have a measured quantity like temperature, or weight, it can vary according to measurement sometimes.(adsbygoogle = window.adsbygoogle || []).push({});

It says for example if I measure a number with a ruler and it goes by units of 1, between 1 and 2, like 1.5. Both are significant numbers, yet according to the book (and since 5 is a non zero I think). The .5 in 1.5 can vary depending on measurements. Why is it then a significant number? If the .5 in the number is uncertain?

From my book it says: Significant figures are all the digits including the estimated digit.

Does this make any sense? Maybe i'm confusing significant numbers with measured or exact numbers, but, I really want to knowwhatmakes numbers significant.Not just that they are. I thought significant numbers had to do with uncertanity measureing them, versus an exact number.

Thanks much for the help.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Significant numbers used in chemistry confusion

**Physics Forums | Science Articles, Homework Help, Discussion**