Man pages matching name qwtscalemap in section 3:

QwtScaleMap.3.en	debian 10 / libqwt-doc
QwtScaleMap.3.en	debian 10 / libqwt5-doc
QwtScaleMap.3.en	debian 11 / libqwt-doc
QwtScaleMap.3.en	debian 12 / libqwt-doc