The invention relates to a method for fabrication of a balance spring of a predetermined stiffness comprising the steps of fabricating a balance spring in dimensions of increased thickness, determining the stiffness of the balance spring formed in step a) in order to remove, locally, a volume of material, in order to obtain the balance spring having the dimensions necessary for said predetermined stiffness.

A method for determining an imbalance characteristic of a hairspring (5) balance (4) oscillator (3) of a timepiece movement (2), the method comprising at least the following steps: Setting the hairspring balance oscillator in an oscillating motion at at least two amplitudes, Determining, for each amplitude and for at least two positions of the oscillator, a piece of data representative of the oscillation period of the oscillator, Using the data from the previous step to calculate the imbalance characteristic of the hairspring balance oscillator.

The invention relates to a method for fabrication of a balance spring of a predetermined stiffness comprising the steps of fabricating a balance spring in dimensions of increased thickness, determining the stiffness of the balance spring formed in step a) in order to remove, locally, a volume of material, in order to obtain the balance spring having the dimensions necessary for said predetermined stiffness.