The Weights and Measures Converter currently returns no results for me for the "12,000 stadia" referred to in Revelation 21:16. However, "12,000 stades," will deliver a result. Given the fact that both ESV and NIV are popular translations and both use the plural "stadia" in Revelation 21:6, shouldn't the WMC be tweaked by the dev team to give us results for "stadia?"