
 Posts: 66
 Joined: Wed Mar 19, 2008 2:18 am
 Location: St. Louis, MO
Let's say I need to determine the average weight of 10 dosage units. Each individual dosage weighs about 3 grams. I weigh each of the 10 individually on a four decimal balance, and get an average of 3.0124 grams (by adding up the individual weights and dividing the total by 10, rounding to 4 decimals because that's the most precise measurement). My coworker, Steve, reviews my work and says that the guiding method states to weigh all 10 at once and report the average; he then repeats the experiment, putting all 10 on the balance at once; he gets a total of 30.1243 grams, divides by 10 to get 3.01243 grams as the average (because he had 6 significant figures to work with). Another coworker, Mildred, reviews Steve's work, but says the average is 3.0124 because one cannot add precision to the measurement and the balance is only precise to 4 decimals.
Our guiding SOP states to use the significant figures rules and not round until the final reportable value, but is quiet on this specific circumstance.
Who has the right weight, Steve or Mildred? What is the right number of significant figures?