These old Brel & Kjr 2107 units are incredible pieces of analog engineering, but they definitely get finicky with age. If your frequency response or filter sweeps are tracking inconsistently, it's usually down to dried-out electrolytic capacitors in the power supply or dirty contacts on the range switches. Give the mechanical contacts a thorough clean with some DeoxIT before adjusting any internal pots.
If you are trying to verify its filter accuracy and don't have a second calibrated hardware analyzer handy, it can be helpful to cross-reference your sweep measurements digitally. You can look at a modern <ahref="
https://noisemeter.co/sound-spectrum-analyzer/">sound spectrum analyzer</a> software setup just to map out the audio spectrum and check if the B&K hardware is actually centering on the correct harmonic bands.
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https://www.electrondepot.com/repair/bruel-kjaer-2107-frequency-analyzer-111868-.htm
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