HP 83491A User Manual page 48

Reference
Cleaning Connections for Accurate Measurements
Figure 4-6. Clean, problem-free fiber end and ferrule.
Figure 4-7. Dirty fiber end and ferrule from poor cleaning.
Figure 4-8. Damage from improper cleaning.
While these often work well on first insertion, they are great dirt magnets. The
oil or gel grabs and holds grit that is then ground into the end of the fiber.
Also, some early gels were designed for use with the FC, non-contacting con-
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