Large stellar surveys of the Milky Way require validation with reference to a
set of "benchmark" stars whose fundamental properties are well-determined. For
metal-poor benchmark stars, disagreement between spectroscopic and
interferometric effective temperatures has called the reliability of the
temperature scale into question. We present new interferometric measurements of
three metal-poor benchmark stars, HD 140283, HD 122563, and HD 103095, from
which we determine their effective temperatures. The angular sizes of all the
stars were determined from observations with the PAVO beam combiner at visible
wavelengths at the CHARA array, with additional observations of HD 103095 made
with the VEGA instrument, also at the CHARA array. Together with
photometrically derived bolometric fluxes, the angular diameters give a direct
measurement of the effective temperature. For HD 140283 we find {\theta}_LD =
0.324+/-0.005 mas, Teff = 5787+/-48 K; for HD 122563, {\theta}_LD =
0.926+/-0.011 mas, Teff = 4636+/-37 K; and for HD 103095 {\theta}_LD =
0.595+/-0.007 mas, Teff = 5140+/-49 K. Our temperatures for HD 140283 and HD
103095 are hotter than the previous interferometric measurements by 253 K and
322 K, respectively. We find good agreement between our temperatures and recent
spectroscopic and photometric estimates. We conclude some previous
interferometric measurements have been affected by systematic uncertainties
larger than their quoted errors