The small signal gain variation over a specified frequency range of an
amplifier at a fixed base plate temperature within the amplifier operating
temperature range. Gain flatness is expressed as + some limit (in dB) from
the nominal gain level. For example, an amplifier with a small signal gain
flatness specification of +1.0 dB would have a maximum of 2.0 dB
peak-to-peak gain variation over its frequency range.