Machine Performance
A vertical line is a needle. A repeating horizontal mark is a feeder. Measuring the repeat tells you which drawer to open.
— no.
Counting from the datum in the direction of numbering
The needle number is only as good as the datum: it must be measured on relaxed fabric from a marked reference wale, and tubular fabric that has been slit, stretched or finished has moved relative to where it was knitted. Compare the defect repeat against the feeder count first — a repeat equal to the number of feeders indicates a single feeder rather than a needle, and no amount of needle-changing will fix it. Sinkers, cams and a burred needle in an adjacent track all produce marks near the calculated position, so treat the number as where to start inspecting rather than as a diagnosis.
Knitting Machine Defect-to-Needle Correlation Analyzer — free, with the formula and a worked example, at Textile School.