Method for adjusting the oscillation frequency of a sprung balance assembly

A method for adjustment the oscillation frequency of a timepiece sprung balance assembly formed at random from among a total output of balance springs and an output of balance wheels, characterized in that, to obviate the need for any grading of the balance wheels and balance springs:

• the means of producing said balance springs is set to a predetermined mean value, and said balance spring production means is set to limit the sample standard deviation of said balance spring output to a predetermined maximum value,
• the means of producing said balances is set to a predetermined mean value, and said balance production means is set to limit the sample standard deviation of said balance output to a predetermined maximum value and within a given unbalance tolerance for said total population of balances,
• to produce the output:
• on the one hand of a single batch of balance springs of a given type, whose mean is capable of a given oscillation frequency for a predetermined balance wheel inertia, each of said balance springs being finished, cut for pinning up to the stud and ready for assembly, and forming a single population of balance springs whose sample standard deviation is peculiar to said single batch output concerned,
• and on the other hand a single batch of balances of a given type, whose mean is capable of said given oscillation frequency for a predetermined balance spring torque and forming a single population of balances whose sample standard deviation is peculiar to said single batch output concerned,
• the manufacturing parameters are determined in accordance with normal production laws for said balances and said balance springs in order to classify said balance population mean according to said balance spring population mean, so that there exists a difference corresponding to a maximum allowable value of the decrease in inertia for each said balance, between the extreme values of:
• on the one hand the gaussian distribution of theoretical frequency values for each balance as a function of said reference balance spring torque,
• and on the other hand the gaussian distribution of the theoretical frequency values for each balance spring as a function of said reference inertia of the balance,
• a random balance spring sample is taken from said single balance spring batch, and a random balance sample is taken from said single batch of balances,
• if necessary, machining is carried out to adjust the poising of said balance sample to bring it within a given poising tolerance, and a complementary inertia adjustment operation is carried out, as a function of the torque value of said balance spring sample, in order to form a sprung balance assembly capable of oscillating at said oscillation frequency after said inertia adjustment operation has been performed on said balance.