Single shots are noisy. Use small shot sets and threshold-based interpretation so drift over days translates into clear actions.
Build a usable baseline set
Pull at least 5 shots with the same dose and target yield before trusting a baseline. Three can be directional, but five is stronger.
Track median time and taste pattern, not just one best shot, then store that as your reference profile.
Interpret drift with concrete thresholds
If median time shifts faster by 3 seconds or more over recent shots with same settings, move grind finer one micro-step and retest.
If median time shifts slower by 3 seconds or more, move grind coarser one micro-step. If shift exceeds 6 seconds, use 2 micro-steps.
Translate trends into next-shot actions
Fast-time plus sour trend means increase extraction: finer grind first, then plus 1 to 2g yield if still sour in band.
Slow-time plus bitter trend means reduce extraction: coarser grind first, then minus 1 to 2g yield if still bitter in band.