A pioneer in the measurement of galaxy rotation curves was Vera Rubin. In the 1970s she used image tubes and measured the spectra using a microscope.
Examples of Rubin's long-slit spectra near H
and the resulting measured rotation curves. They exhibit the now-classic shape: (rapid) rise from the nucleus to a maximum velocity that is maintained roughly flat to the largest radius measurable.
More examples of Rubin et al's rotation curves, showing a little more of the true variation. (Rubin et al 1978 ApJ 225 L107).