What the browser reports
The browser location interface can supply speed in meters per second. A value of zero is valid; a missing speed is represented by null. Xpeed keeps that distinction instead of converting every missing value to zero.
When valid positions and timestamps are available but direct speed is missing, the tool can estimate distance divided by time. That fallback has its own label because it is a different source.
Position accuracy is not speed accuracy
The accuracy field describes uncertainty in the reported position, in meters. It is not a plus-or-minus error margin for speed. Xpeed displays it to provide context without claiming it validates the speed number.
Two uncertain positions can produce an unstable distance estimate, especially over a short interval. This matters at low walking speeds and while standing still.
How Xpeed handles gaps and jumps
The measurement core rejects invalid coordinates, repeated or reversed timestamps and implausible changes under its documented engineering limits. Missing periods stay as gaps rather than straight-line distance.
Displayed smoothing is separate from accepted trip statistics. Maximum speed is calculated from accepted measurements, not from an animated dial position.
Read average speed with its time basis
Trip average and moving average answer different questions. Elapsed time can include accepted-session stops; moving time counts accepted movement. A pause or signal gap changes which intervals are available.
Unit changes convert the same underlying SI values. More decimal places would not make the original measurement more accurate.
What has been verified
Automated tests check formulas, missing data, timestamp order and lifecycle behavior using synthetic samples. They do not prove field accuracy or compatibility with every phone.
No Xpeed field test on an aircraft, boat, train or specific phone is claimed here. Use a suitable calibrated instrument when a decision depends on a measured error bound.