The jitter could be anything. PlexTools has a floating Y-axis for jitter, so you only see relative jitter values.
You might consider using PxScan/PxView instead, which will show you "absolute" jitter values that makes it possible to compare between discs scanned on the same drive. The "absolute" values cannot be compared between individual drives, however, and the lower the absolute value the higher the jitter (which is why the Y-axis is inverted for jitter scans using PxScan/PxView). There is no known formula to transform the PxScan jitter values to a percentage, but at least it beats the floating Y-axis of the PlexTools scan.