Sample, survey, or instrument

Use a defined population and a defensible measuring tool, and show the uncertainty instead of hiding it.

Six months into learning Spanish, you can't tell whether you're improving. Some days you chat with the neighbor and feel fluent; some days you blank on the word for fork. You're about to judge half a year of work by your most recent bad conversation, which is a terrible measuring device.

The move is to use a defined population, a defensible measuring tool, and visible uncertainty instead of vibes. The cue is realizing your "measure" changes every time you look. Steps: pick a real instrument (a standardized placement test, or a fixed list of 100 words and phrases you care about), define what it samples (conversational vocabulary, not literary Spanish), take it under the same conditions each time, and record the score as a range rather than a single number, since retakes wobble. When it works, "am I getting better?" becomes a number with error bars you can compare against next quarter's number. Don't use it when the instrument measures the wrong target; a grammar test that ignores speaking will steer your study toward the test, and for a trivial choice a quick gut check is honestly enough.