What I meant by timing was covering a known mile in 60 seconds at 60 MPH, like using mileposts on the highway to gauge distance. As long as you are covering one mile every 60 seconds at 60 MPH, you know the speedo is accurate while your odometer is registering only 3/10 miles. If you were going farther than, or less than a mile every 60 seconds, then we know the speedo is off too. Either way sounds like the speedo head needs to be rebuilt to repair the odometer. No telling how long it has been recording inaccurate mileage. Have you tried to contact the prior owner, might be this is something that recently came up.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.