For a harmless local comparison, choose one repeatable software action such as opening the same sample file, running a development-only formatter and viewing its result. Start immediately before the first action and press Lap after each completed repetition.
Keep the comparison conditions visible
Use the same sample, device, browser state and number of repetitions. Close unrelated work if that is part of the chosen protocol, but do not claim the browser stopwatch isolates CPU scheduling, disk cache, network activity or thermal state. The lap table is an observation of this session, not a benchmark certificate.
Export before starting the next run
Pause after the final completed lap, download CSV and identify the run in your own notes. Reset only after checking the downloaded rows. For another configuration, create a new session and another file so lap numbers cannot silently cross configurations. Compare distributions or repeated splits outside LapWatch rather than treating one fastest row as a general result.
Know what the browser cannot promise
LapWatch is an informal in-page instrument, not an independent clock service. Closing or reloading the page clears every timestamp and lap. Device sleep, browser suspension and operating-system differences can affect what one browser reports. Keep another suitable method whenever the duration matters, and never use this tool for medical, emergency, food-safety, transport, industrial, official, legal or other safety-critical timing. The fixed 99:59:59.999 and 500-lap limits prevent a forgotten tab from pretending to provide unlimited continuity.