  M55 (NGC 6809) and NGC 6362 are among the few globular clusters for which
masses and radii have been derived to high precision for member binary stars.
They also contain RR Lyrae variables which, together with their non-variable
horizontal-branch (HB) populations, provide tight constraints on the cluster
reddenings and distance moduli through fits of stellar models to their
pulsational and evolutionary properties. Reliable (m-M)_V estimates yield M_V
and M_bol values of comparable accuracy for binary stars because the V-band
bolometric corrections applicable to them have no more than a weak dependence
on effective temperature (T_eff) and [Fe/H]. Chemical abundances derived from
the binary mass-M_V relations are independent of determinations based on their
spectra. The temperatures of the binaries, which are calculated directly from
their luminosities and the measured radii, completely rule out the low T_eff
scale that has been determined for metal-deficient stars in some recent
spectroscopic and interferometric studies. If [alpha/Fe] = 0.4 and [O/Fe] = 0.5
+/- 0.1, we find that M55 has (m-M)_V = 13.95 +/- 0.05, [Fe/H] = -1.85 +/- 0.1,
and an age of 12.9 +/- 0.8 Gyr, whereas NGC 6362 has (m-M)_V = 14.56 +/- 0.05,
[Fe/H] = -0.90 +/- 0.1, and an age of 12.4 +/- 0.8 Gyr. The HB of NGC 6362
shows clear evidence for multiple stellar populations. Constraints from the RR
Lyrae standard candle and from local subdwarfs (with Gaia DR2 parallaxes) are
briefly discussed.
