Validation of the accuracy and precision of<i>Gaia</i>EDR3 parallaxes with globular clusters

CONTEXT. Gaia EDR3 has produced parallaxes for 1.468x10^9 sources but there are calibration issues that require corrections to the published values and uncertainties. AIMS. We want characterize behavior of uncertainties parallaxes. also aim provide a procedure calculation distances stars stellar clusters. METHODS. reanalyze some data in papers QSO LMC combine those results with measurements six bright GCs. calculate angular covariance at small separations based on it larger angles using QSOs obtain an analytical formula over whole sky. The GCs used validate parallax bias correction as function magnitude, color, ecliptic latitude determine constant convert internal external ones. RESULTS. zero separation is 106.2 muas^2, yielding minimum uncertainty 10.3 muas individual stars. That value can be only slightly reduced after considering separations. Lindegren et al. works quite well, except brighter magnitudes, suggesting improvements may possible there. k 1.1-1.7 depends G. Stars moderately large RUWE still useful albeit k. give accurate precise specific case 47 Tuc we able beat limit derive high-precision distance 4.53+-0.06 kpc. Finally, recipe derivation clusters given. [ABRIDGED]