Rate adjusting method of mechanical timepieces

A rate adjusting method for a mechanical timepiece comprised of a movement having a mainspring constituting a power source for generating a rotational force, a front train wheel for undergoing rotation by a rotational force generated by the mainspring, and an escapement and speed control apparatus for controlling rotation of the front train wheel, the escapement and speed control apparatus having a balance for undergoing reciprocal right-hand rotation and left-hand rotation, an escape wheel and pinion for undergoing rotation in accordance with rotation of the front train wheel, and a pallet fork for controlling rotation of the escape wheel and pinion in accordance with rotation of the balance, the balance having a hairspring, a balance stem and a balance wheel, the rate adjusting method comprising the steps of:

• assembling the movement of the mechanical timepiece;
• disposing the assembled movement in a vertical position and measuring rates with respect to a plurality of vertical attitudes of the assembled movement;
• calculating the magnitude and direction of an attitude difference vector in accordance with the measured rates;
• calculating a weight amount to be added to or subtracted from the balance wheel and calculating a position on the balance wheel where the amount of weight is to be added or to be subtracted in accordance with the calculated magnitude and direction of the attitude difference vector;
• and
• adding to or subtracting from the calculated position of the balance wheel the amount of weight in accordance with the calculated weight amount and the calculated position on the balance wheel.