Various effective temperature scales have been proposed over the years .
Despite much work and the high internal precision usually achieved , systematic differences of order 100 K ( or more ) among various scales are still present .
We present an investigation based on the Infrared Flux Method aimed at assessing the source of such discrepancies and pin down their origin .
We break the impasse among different scales by using a large set of solar twins , stars which are spectroscopically and photometrically identical to the Sun , to set the absolute zero point of the effective temperature scale to within few degrees .
Our newly calibrated , accurate and precise temperature scale applies to dwarfs and subgiants , from super-solar metallicities to the most metal-poor stars currently known .
At solar metallicities our results validate spectroscopic effective temperature scales , whereas for \mathrm { [ Fe / H ] } \lesssim - 2.5 our temperatures are roughly 100 K hotter than those determined from model fits to the Balmer lines and 200 K hotter than those obtained from the excitation equilibrium of Fe lines .
Empirical bolometric corrections and useful relations linking photometric indices to effective temperatures and angular diameters have been derived .
Our results take full advantage of the high accuracy reached in absolute calibration in recent years and are further validated by interferometric angular diameters and space based spectrophotometry over a wide range of effective temperatures and metallicities .