HP 8712ET User Manual page 158

Using Instrument Functions
Using Limit Testing
Example 1
When using a small number of measurement points, limit lines must be
set carefully, or the results may be confusing. The following illustration
shows a data trace with three measurement points: A, B, and C, along
with a minimum limit line.
Figure 4-17 Limit Lines Example 1
Note that the beginning of the limit line falls between points A and B
along the horizontal frequency axis. The end of the limit line falls
between points B and C along the frequency axis. Therefore, only one
measurement point is encountered between the beginning and end of the
limit line. This particular example would result in a limit test result of
"PASS" when it appears that it could fail. More measurement points are
needed to evaluate this measurement.
4-40 ET User's Guide