The Damasko "Si" chronograph movements are based on the ETA 7750
movement. The escapement is replaced with an escapement made in
house by Damasko. The new escapement uses a poly-silicon (chemical
symbol "Si") balance spring, hence the "Si" label.
Member YPO posted photos of the Damasko DC66 Si and the DC67 Si.
YPO photo of DC66 Si
YPO photo of DC67 Si
The Damasko "Si" chronograph specifications