I just estimate it based on the times listed when the GPS is collecting data. Very low tech!
Funny, that skeg has been gone since 2009. I put a stainless cover over the missing bit and run it! Good thing too, cuz my crane was not high enough to remount the motor and long shaft! First time I took that cover off to get me 5 more inches! I’m waiting for new bolts from Amazon today to replace it. Another lower is in my future…