Graduation scale having a continuous planar surface with a protective diffusion barrier layer thereon

A length or angle measuring instrument comprising:

• a first grating graduation for diffracting a beam of light;
• a carrier member having a phase graduation thereon in a graduation region of the carrier member wherein the graduation has graduation structures spaced apart from one another in the graduation region, the graduation structures having transmission properties different from that of carrier member wherein the graduation is an integrated component of the carrier member and forms a continuous planar surface in the graduation region, wherein said continuous planar surface has a protective diffusion barrier layer thereon, the graduation of the carrier member further diffracts the beam of light passed through the first graduation;
• a second grating graduation for bring the diffracted beams from the carrier member into interference;
• and
• detectors for detecting the interference.