Every flight log the Nano saves carries a built in verification signature, so anyone can confirm a log is genuine and exactly as the altimeter wrote it. A real, unedited log passes; if anything in the file has been changed, even by a single character, it fails. This page just shows the ways to check a log. For how the signature works and why it matters, especially for competition, see the security page, and for getting the most out of your flights, see the Altimeter Cloud page.
The easiest way is the verify tool on Altimeter Cloud. Open the upload page, add your CSV flight log, and it will tell you straight away whether the log is genuine. This is also what happens automatically whenever you upload a flight to your account, so a log that has been edited will simply be turned away.
iGOOD TO KNOW
Because every upload is checked this way, any flight you can see on Altimeter Cloud has already passed verification and is a genuine, unedited log. That is reassuring when you are looking at someone else's result, a competitor's for instance: if it is on Altimeter Cloud, it has been verified.
If you want to check logs in your own software, for example as a competition organiser processing many entries at once, you can post the unedited CSV flight log to our public verification API. It needs no sign in and has no rate limit. Send the whole file as the csv parameter in a POST to https://www.altimetercloud.com/api/csv_verify/ and it returns a simple result telling you whether the log passed, along with a few details such as the apogee and a unique flight identifier.
The full response format, the error codes, and a live playground to try it in your browser are on the API page.