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tokens: of the AM CVn (= SDSS J120841.91+355024.8), two polars (AR UMa in a low state and AP CrB in a high state), and three dwarf novae of the sub-types U Gem, SU UMa, and WZ Sge (= GY Cnc, BZ UMa, and EZ Lyn, respectively) were obtained from SDSS DR16 (Ahumada et al. 2020 ). CV subtypes : The CV Gold Sample contains examples of all six major different sub-types, their respective numbers are listed in Table 4 . The different sub-types form clearly distinct clusters in the Gaia HR diagram (Fig. 8 , left-hand panel); 6 and the location of these clusters closely links to the spectro-photometric properties of each sub-type (Fig. 8 , right-hand panel). Table 4. The number of each type in the CV Gold Sample together with the range of their orbital periods. The novalike variables are characterized by stable high mass transfer rates and hot accretion discs that dominate the optical emission of these systems. Correspondingly, their cluster is located at small absolute magnitudes and blue colours. Two AM CVn stars, HP Lib and the prototype AM CVn itself (Faulkner, Flannery Warner 1972 ) are novalike variables with stable, hot helium discs that are somewhat bluer and fainter than their cousins with hydrogen-rich discs. The three sub-classes of dwarf novae exhibit clear trends in their location within the HR Diagram. The U Gem type dwarf novae have lower mass transfer rates than the novalike variables, their quiescent discs are therefore less luminous and their donor stars can contribute noticeably to the optical flux of the systems, which is reflected in the number of these systems being located close to the main sequence. The donors and accretion discs in the SU UMa systems are less luminous than those in U Gem-type dwarf novae, hence they are concentrated closer to the white dwarf cooling sequence. Finally, the WZ Sge type dwarf novae have the dimmest accretion discs and donor stars; in fact, some of them contain brown dwarf companions (GD552 Unda-Sanzana et al. 2008 ; QZ Lib (Pala et al. 2018 ), 1RXS J105010.3–140431 (Mennickent et al. 2001 ), SDSS J102905.21+485515.2 (Thorstensen, Alper Weil 2016 ), SDSS J143317.78+101123.3 (Hernández Santisteban et al. 2016 ), and SSS J122221.7–311525 (Neustroev et al. 2017 )). WZ Sge are therefore inherently the faintest CVs and merge into the white dwarf cooling sequence. A noticeable outlier among the dwarf novae is V1129 Cen, a long-period (≃21.4 h) CV that exhibits low-amplitude (≃0.6 mag) outbursts about once per year, but no emission lines are detected in its spectrum (Bruch 2017 ). The donor is a luminous F-type+ star, explaining the location in the HR diagram. Magnetic CVs have a larger spread due to their more varied spectral appearances. During states of low mass transfer they resemble the detached WD+M binaries whilst during high states, their optical spectra can contain cyclotron emission lines (Wickramasinghe 1988 ) that will affect their colour and absolute magnitude. Overall, the CV Gold Sample contains a