If you want to measure in the circunferencial direction you need a perfilometer, but in a turning bar you need to measure in axial direction to "cut" the lines made by the point cutting tool. In this case you can use a normal rugosimeter.

Excuse me Sir, you need to measure "during turning operation?".

For what reason do you need to measure the roughness in the circunferential direction?

You need to measure in axial direction. This is the maner. I measure many times in this manner and dont have any problems.

Here do you have some examples of the roughness measure method over cylindrical surface.