I remember ADIs from 40 years ago with a fast/slow bug on the left side like
this . Is that what you were referring to, safetypee? The reference speed was set by the pilot from the bug on the ASI with alpha protection at low speed on the approach. Khalid's reference is probably from a new EASA syllabus LO, though, which says "Explain the following vertical modes: vertical speed (V/S); flight path angle (FPA); level change (LVL CHG)/open climb (OP CLB) or open descent (OP DES); speed reference system (SRS); altitude (ALT) hold; vertical navigation (VNAV)/managed climb (CLB) or descent (DES); glideslope (G/S)." and therefore unlikely to be an old system.