Frequency adjustment method for piezoelectric resonator device

A frequency adjustment method for a piezoelectric resonator device, wherein the piezoelectric resonator device comprises a tuning-fork piezoelectric resonator piece having a pair of resonator arms and a metallic adjustment film formed on each of the resonator arms, and wherein a frequency is adjusted by reduction of a mass of the metallic adjustment film,

• the frequency adjustment method comprising:
• a rough adjustment of roughly adjusting the frequency by partially thinning or removing the metallic adjustment film;
• and
• a fine adjustment of finely adjusting the frequency by at least partially thinning or removing a product derived from the metallic adjustment film that has been thinned or removed in the rough adjustment,
• wherein the piezoelectric resonator device that accommodates the tuning-fork piezoelectric resonator piece has a generally rectangular shape in plan view, with plane external dimensions of the piezoelectric resonator device being 1.6 mm or less on long sides and 1.0 mm or less on short sides, and
• wherein the metallic adjustment film has a thickness in a range from 0.003 mm to 0.020 mm before the rough adjustment.