Rate: -006 s/d
Amplitude: 309*
Beat Error: 0.3ms
60 seconds a min, x 60 an hour x 24 hours=86400 seconds a day so -6 a day as a percentage is 0.00694% error, is not bad and infact good for any non chronometer movement
the amplitude is the degrees of movement that the balance wheel is moving and 309 is good for that movement
the beat error is the difference in time in milliseconds that the the impulse stone causes the paletes to lock and unlock the escape wheel, think of it as a limp, one leg is slower than the other by 0.3ms and 0.3 is nothing to worry about,
But remember that a mechanical movement is affected by many things such as:-
the power in the main spring, fully wound or low power reserve
the watches position and orientation
temperature
servicing and clenliness