Select a meaningful record window
The workbench numbers decoded record messages in source order. First and last record controls define an inclusive selection for CSV and GPX. This is useful for excluding an unrelated tail or focusing on the portion of an activity that still has reliable timestamps. The preview shows up to one hundred rows while the downloads contain the full selected range.
If timestamps repeat or run backward, review the finding before enabling the optional filter. The filter keeps the first record and then omits timed records whose timestamp does not increase beyond the last retained timed record. Omitted record numbers remain in the selection audit. It does not invent replacement times or reorder the original sequence.
Understand the narrower GPX model
GPX carries timed coordinates and optional elevation in this tool. It does not carry FIT power, cadence, heart rate, lap summaries or developer fields. CSV exposes a documented standard sensor subset and the source byte offset of each record. The unchanged prefix FIT is the appropriate output when retaining original unknown message bytes matters.
A missing or invalid coordinate is not replaced with zero. Untimed points are not assigned guessed timestamps. Such points are omitted and split the GPX track. A time reversal or gap over five minutes also starts a new segment. Read the resulting point and segment counts before interpreting distance or pace in another application.
Keep projection and recovery separate
Record selection does not apply to the prefix FIT download. Filtering FIT records while retaining untouched session and lap totals would create a misleading activity. The workbench therefore names that export explicitly and requires acknowledgement of its limits before generating it. It preserves all complete messages up to the first parsing failure.
Download the selection audit next to the GPX or CSV. It records the source checksum state, selected range, omitted records and projection boundaries. If you import CSV into a spreadsheet, review automatic type conversion and retain UTC timestamps. Recheck a few coordinates and sensor values against the original device display or another independent reader when possible.