I liked to measured the freq-. response of my wide-band 20..40dB amplifier.
So the tracking gen., as a maximal of a maximal of 20dB attenuation supported, I did run into into an input level overdraft.
This is IMHO a very hard limitation/restriction.
So it required, to attenuate the tracking generator, to more than the allowed maximal of 20dB.
hp