For sale, a high-precision arc protractor for cartridge alignment. This protractor is made of 3mm high-quality acrylic, coated with a yellow film, and high-precision laser-cut and engraved. The first picture is for reference only; the real protractor looks like the one in the second and third pictures.
The arc protractor is the most accurate protractor for cartridge alignment; this one is designed for the following SME tonearms:
M2-9
M2-9r
Series III modified
Series IV
Series V
How to spot if you have a modified SME series III:
 
It's simple; the headshell is different, the unmodified version has 15 holes on the top of it (apart from the two fixing holes), while the modified version has 11 holes.
 
The geometric features are compliant with SME specifications; see the first picture.
It is supplied with detailed instructions.
We also make custom protractors to the client's specifications.