HHonza,
Since each BB60C has different calibration data which controls the sensitivity of the receiver based on the reference level, it is possible for the same reference level to provide different gain/attenuation settings. A good test would be to set the reference level to -50dBm, match RBW/VBW/center freq and measure the level of the noise floor (trace averaging can help). You can also manually control the gain/atten by enabling the manual gain/atten settings (file menu).
Feel free to email justin@signalhound.com with any more information or pictures.
Regards,
Andrew
