Bug report: the reconstitution calculator and a rounding edge case — setting out what I have, and where I think it stops being reliable.
Posting the calculation with the inputs, so that somebody can disagree with a step rather than with the answer.
Inputs: 5 mg in 1 mL, target 1.0 mg, U-100 barrel. Working shown below in the order I did it.
I have checked it twice by the same route, which is not the same as checking it twice.
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.
Somebody will have a better source than mine, and I hope they post it.
Understood. Thank you for being specific about the limits of it.
Post #3 is the version of this I will quote in future. One addition.
The most common input error is entering the vial mass in the concentration field. It produces a plausible number, which is why it survives.
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.
Not the answer, but possibly the question that gets there.
Maintaining a calculator means checking the arithmetic against hand-worked cases at each review, not checking that it still loads.
Written from notes rather than memory, which is why the numbers are specific.
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.
The interesting part of this is the exception, and I do not understand the exception.
Coming back to post #10, because the follow-up matters more than the original answer.
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.
I would hold that lightly until someone with a larger sample weighs in.
Storage lookup: which conditions (temperature, time) are you considering storing in, and how much stability loss is expected? The calculator gives a rough estimate based on typical stability data. Not a substitute for your compound's specific stability data.
Two sources, same conclusion, and I could not rule out that one copied the other.
Why calculators are not medical advice: they do arithmetic. Medical decisions are not arithmetic. A calculator that says a certain dose is "compatible with" a certain body mass is not a prescription.
It cost nothing to check and would have cost something not to.
Post #12 answers the question as asked. The question underneath it is different.
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.
This is the sort of thing that ought to be settled and apparently is not.
Do the arithmetic by hand the first few times, whatever tool you use afterwards. A calculator with a wrong input gives a confident wrong answer and there is nothing in the interface to tell you.
This is the sort of thing the wiki should carry and currently does not.
I came in to disagree and I am leaving without a disagreement.
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.
Where a calculator and your own arithmetic disagree, the productive move is to find which step differs rather than to decide which is right.
If the premise is wrong, everything after it is decoration.
Nothing a calculator produces is medical advice, and a correct calculation on inappropriate inputs is still an inappropriate answer.
The claim is narrower than it sounds, and deliberately so.
The reconstitution calculation is total mass divided by total volume for concentration, then dose divided by concentration for volume, then volume times one hundred for units on a U-100 barrel. Three steps, and every error is in one of them.
Anyone who has looked at this more carefully, please correct the record.
This is the sort of exchange that makes the archive worth searching.
Where I part company with post #19, and it is a narrow parting.
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.
Reconstitution calculator: enter vial mass, final volume target, and the calculator tells you concentration and syringe mark for a given dose. Useful for double-checking arithmetic when you are doing it by hand.
That holds under the stated conditions and I have stated them.
I had written a reply contradicting post #23 and deleted it. Here is what survived.
Nothing a calculator produces is medical advice, and a correct calculation on inappropriate inputs is still an inappropriate answer.
The honest answer is that it depends, and here is what it depends on.
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.
Take the reasoning and check the arithmetic; I do not always get it right.
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.
Picking up post #27: that is the part I would want checked first.
Where a calculator and your own arithmetic disagree, the productive move is to find which step differs rather than to decide which is right.