I'm tinkering around with an early 90's Cannondale M300 mountain bike. The rear derailleur is a Shimano Altus C10 and the front derailleur is a Shimano Altus A10. The limit screws on both derailleurs are not marked with H or L. Can someone tell which screw is which on both derailleurs? Is there an easy way to identify them if not marked or perhaps a rule of thumb? Thanks in advance for any feedback.