[Test-Equipment] HP-606A Calibration question

[Barry]

I was just looking into this again and I notice that there are two 
independent slugs for the 530kc to 1800kc range (and other ranges too).  I 
had not noticed this before.  The manual makes no mention of separate 
adjustments.  What's the proper way to set both slugs?  Is it possible this 
is what is causing the linearity problem (one or both slugs is not in a 
correct position)?

Barry - N4BUQ