The mass-error checker and its intended scope

The mass-error checker and its intended scope Writing it up because I had to work it out twice and would rather nobody else did.

Proposing that mass-error checker deserves a maintained page rather than a recurring topic, and drafting the skeleton here so that the argument about scope happens before the writing rather than after.

What I think belongs on it, what does not, and the three claims that would need a citation each.

I would be cautious about generalising from the mass-error checker example above. It is a good example. It is one example.

On mass-error checker, the part that usually goes wrong is that the question is asked as though it has one answer. It has a range, and the width of the range is the interesting bit.

If you can post the two or three numbers you are working from, several people here will check the arithmetic rather than argue about the conclusion.

A calculator that shows its working is worth ten that give an answer. The whole value is being able to see which step you disagree with.

What I would check first on mass-error checker is whether the thing being measured moved or whether the way of measuring it moved. Those look identical in a graph.

Unit-conversion tools are only as good as the assumption they make about the syringe. Ask what barrel and what graduation interval it assumed before trusting the units figure.

Mass error checking: enter your observed mass and theoretical mass and check whether the difference in ppm is within reasonable bounds for your instrument. Useful sanity check on LC-MS results.

The part I am sure of is shorter than the part I have written.

Post #122 is right about the mechanism and I think understates the practical bit.

Significant figures in the output should not exceed what the inputs support. A concentration calculated from a nominal vial mass is not known to four decimal places.

The bit of mass-error checker that nobody enjoys is that the answer changes depending on what you are trying to decide with it. Say what the decision is and the thread will converge.