Are these expressions to call of a particular kind of deviation right?

I am translating a material on visual sensors and having a hard time figuring out what to call this.

The situation is that when the sensor senses a circle mark, sometimes it does not detect a fine circle. Instead, the circle becomes a little wavy, having some parts of outline sticking out of the real line, and some parts going inside.

I need to express the length of the difference between the real line and the off-points of the detected line. I came up with the following two expressions. Does either of them indicate what I am trying to say?

Positive/negative difference” OR “Positive/negative deviation length”.

I think simply "deviation" is fine. Deviation is already defined as "a measure of difference between the observed value of a variable and some other value".

So I'm pretty certain you don't even need the "length"-part. The term "deviation in length" is only used when referring to an actual difference in length.

I'd go for "The deviation between the two lines in [unit] is X".