In this specific case it is AM Caliber 520...529 movement.I was interested to find right designation so I can order new balance staff.
If you look table sheet in link that is kindly provided by Roland you can see that AM movements from 480 to 546 all have same or similar style bridges but ligne size and height of movement are not same, also jewels count is from 15 to 17. So You will have to measure movement to determine caliber number.
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