Match the calculation to the question

Every bench calculation and every graph answers one specific question. A dilution factor tells you what a diluted result would have read undiluted. A recovery calculation tells you whether a known spike came back close to what was added. A regression line tells you how one method's results relate to another method's results across a concentration range. None of these substitutes for the others, and reaching for the wrong one produces a number that looks like an answer but is not an answer to the question that was actually asked.

Carryover, drift, nonlinearity, and imprecision are four distinct performance questions, and none of them can be inferred from a single regression result. A method comparison study answers a bias question. A linearity study answers whether a procedure holds a straight-line response across its claimed reportable range. A carryover study answers whether a high result contaminates the next specimen. Mixing these up is a common shortcut, and it produces a conclusion the data was never designed to support.

The workflow below is the same five-step check for any laboratory calculation or graph choice, whether the task is a dilution, a recovery, or a method comparison.

Before you calculate anything, name the exact question you are answering, because the formula and the graph that answer it are not interchangeable with the ones that answer a different question.