Sí, en algún sitio hay un error, o a lo mejor ha habido cambios en las características del modelo y no se ha actualizado la información. Del catálogo de Sinn:
Black Hard-Material Coating
Some Sinn watches,such as
models 756 and 856,are also available in a black
tegimented case variant.This hard-material coating is created by PVD-technology.
Normally,coatings of this type on watches tend to crack because of the large
and abrupt deviation in hardness between the coating and the base material
(eggshell effect).
At Sinn PVD coating is only found on Tegiment cases.
The hardness of Tegiment is comparable to the PVD layer but its hardness
continuously blends into the base hardness of the case.For that reason,the
eggshell effect can be ruled out and wear and tear on the coating can be
reduced drastically (page 155).
Y el 656 negro lo describe así:
Model 656 S with a deep black
chrome-plated
case and choice of leather strap or matching
black bracelet.
En cualquier caso, independientemente de la técnica que usen, es muy bonito