MadSci Network: Chemistry

Re: In the number, 24.090, why isn't the first '0' a significant figure?

Area: Chemistry
Posted By: Robert L. Judge, Faculty, Chemistry/Science Department, Holy Cross High School
Date: Fri Oct 10 17:13:25 1997
Area of science: Chemistry
ID: 876448941.Ch
Mr. Nelson,
	Without reciting the rules for determining significant numbers which 
can be read from the text book, I will attempt to answer your question.  If 
you look at the number carefully you will note that there is a unit of 
measurement at the end of the number, which I noticed is absent from your 
question.  This then becomes the fundamental error.  In science and in the 
particular case at hand, numbers are not theoretical abstractions that 
indicate mearly the magnitude away from the theoretical point on the number 
line of (0,0); but rather have a dual dimension which indicate magnitude 
and  (and this is of utmost importance) the quantity being measured.  In 
the case at hand, the quantity is the mass of something in grams.  This 
number then comes from the concrete fact that something was measured to be 
24.090grams.  Since this is true, the number given as the test question 
demonstrates or indicates that the instrument used to measure whatever was 
measured was precise to  1/1000 of 1 gram and the last digit is understood 
to be estimated.  This you have experienced in the lab yourself.  If the 
instrument used is precise to that degree, then the zeros that comes 
between non zero digits could very well have been any magnitude from 0, in 
this case meaning "zero tenths of a gram" to a magnitude of nine tenths of 
a gram.  The fact that that particular place in the decimal scheme is a 
zero is of no consequence since it could have been any digit as I've noted 
above.  The  zero at the end of the number and to the right of the decimal 
shows the precision of the instrument being used and is understood to be 
estimated.  Again, this zero is not acting as a place holder but could have 
very well been any digit.   Hope this satisfies your curiosity

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