Amplitude is the measurement in degrees of the balance arc of swing. The measurement is the amount of degrees the balance will travel from the point of impulse until the tension of the hairpsring arrests the balance and causes it to return in the opposite direction.
A typical healthy amplitude will be between 270 and 315 degrees, although this will vary depending on the design and grade of the particular watch movement.
The position of the watch movement will also affect amplitude performance. You may find that the arc of swing may be greater if the movement is in the dial-up or dial-down, i.e. horizontal, position. Otherwise, the balance staff pivots will be turning on their sides in the vertical position. This can increase friction and this may reduce amplitude.
The performance may also be affected depending on the state of wind as the mainspring delivers less driving force.
Amplitude is covered in several lessons within our Watch Repair Course.You can learn how to troubleshoot issues with the power source and further fault finding techniques in level 3
The rate of amplitude can be visually observed, however using a device such a timing machine will provide a more accurate determination.
If the amplitude performance of a watch movement is found to be too high, it may be an indication that the mainspring is too strong. In some cases this can be so extreme as to cause knocking of the banking.
Should a watch movement be found to have low amplitude performance, it is a strong indication that the watch movement has issues and will need to be worked on.« Jargon Buster Index