The Balance Wheel in Detail

The balance illustrated is from a Longines pocket watch. The balance is of an older, split, bimetallic design, which is not often used in contemporary watches. The screws around the rim of the balance wheel are used to adjust the poise (“balance”) of the balance wheel, and, in split balances with steel balance springs, the temperature compensation. Such a split balance is made of layered steel and brass and is cut at two points near the balance arms. (1) The impulse roller. (2) The safety roller. (3) The lower

balance pivot
. (4) The impulse jewel (or impulse pin). (5) The balance spring (in this case an overcoil design). (6) The alignment pins used to locate the balance cock accurately on the main plate.