Dating in the dark 8309
DIN guideline 8309 stipulates that mechanical watches are antimagnetic if their rate change does not exceed /- 30 seconds per day after exposure to a magnetic field of 4,800 A/m (corresponds to 6 m T) (movement diameter larger than 20 mm).The watch should also not stop when exposed to a magnetic field of this strength.Multiple layers with different types of coating and thicknesses are required to create an anti-reflective effect at different wavelengths (colours) of visible light.Sinn's sapphire crystals are always coated on both sides to ensure optimum readability.
The average amplitude values of most watch movements made today are between 250° and 300°. DIAPAL Technology deals with this problem at the root, by dispensing with the need for oil altogether.
An older, historical type of balance is the screw balance.
This was first used in the form of the compensating balance which is split at two points to compensate the temperature error; it has a bi-metal construction.
The splitting of the light mentioned above then takes place both on the surface of the glass and also on the surface of the thin anti-reflective layer.
The light reflected from this layer overlaps with that from the glass itself.
The to-and-fro motion of the balance is translated by means of a small ruby pin (ellipse) into to-and-fro rocking of the anchor.