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.
Source for the mass-error checker figure, since it was asked for. It is in the discussion rather than the abstract, which is why the version circulating is stronger than the paper is.
Reading the surrounding paragraph is worth the two minutes. The authors are more careful than their summarisers.
Mass-error checker is one of those subjects where the general answer and the answer for a specific case diverge, and the thread will go in circles until someone says which one is being asked for.
The opening post is the version of this I will quote in future. One addition.
Tools that run entirely in the browser send nothing anywhere, which matters more to some people here than others and is worth stating either way.
The useful distinction on mass-error checker is between what was measured and what was inferred from it. Both end up in the same sentence and only one of them has error bars.
I had written a reply contradicting post #5 and deleted it. Here is what survived.
A saved calculation is worth more than a remembered one. Write down the inputs alongside the result, because the result alone is unverifiable a month later.
Confirming post #5 from a second method, which matters more than confirming it from a second person.
Speaking only to mass-error checker as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.
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.
One case, stated as one case.
Before the thread moves on from mass-error checker — what is the sample size behind the claim? I am not being difficult; I have seen the same figure quoted from an n of four and from an n of four hundred.
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.
Post #10 answers the question as asked. The question underneath it is different.
The confident answers on mass-error checker and the well-sourced answers are not the same answers, which is the most useful thing I have learned reading this category.
Saving this. It is the version I will quote when the question comes round again.
This follows post #13 rather than contradicting it.
For anyone finding this later: the short answer on mass-error checker is that it depends on one thing, and the rest of the thread is people identifying which thing.
Dose equivalence calculator: compounds have different potencies. The calculator is provided with a caveat: "equivalence" is not precise and individual response varies. It is a rough starting point, not a dose prescription.
A partial answer, offered because a partial answer beats none.
The calculators maintained on this site are open-source and verifiable. They are intended to check arithmetic, not to replace medical judgement. Using them is optional and they are provided for convenience.
Coming back to post #16, because the follow-up matters more than the original answer.
Two things can be true about mass-error checker at once: the mechanism is plausible and the evidence for the size of the effect is thin. Most of the argument here is people defending the first against attacks on the second.
Where I part company with post #16, and it is a narrow parting.
Precision and significant figures: the calculators do not round to match your input precision. If you input values to one decimal place, the output might have more. Use significant figures appropriate to your input precision.
Adding it in case it saves somebody the afternoon it cost me.
I had written a reply contradicting post #17 and deleted it. Here is what survived.
I disagree with the framing of mass-error checker above, and I think it is a substantive disagreement rather than a terminological one. Setting out why, so it can be checked.
The reasoning depends on an assumption that is doing a lot of work and is never stated. If the assumption holds, the conclusion follows. I do not think it holds generally.
I came in to disagree and I am leaving without a disagreement.
Practical note on mass-error checker: write down what you expect before you look. The number of times I have found what I went looking for is higher than chance would allow.
The parts-per-million mass-error calculation is simple enough to do mentally to one significant figure, which is a good habit because it catches an order-of-magnitude slip immediately.
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.
What would change my mind on mass-error checker is a second dataset collected by someone with no stake in the first. Until then I hold it loosely and I would rather say so than pretend to more.
Picking up post #25: that is the part I would want checked first.
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.
Noting that the question and the thing people usually mean by it are different.
This settles it for me, at least until somebody posts a reason it should not.
Post #28 answers the question as asked. The question underneath it is different.
I keep a log for mass-error checker specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.