The Numeric Converter tool returns "NaN" (Not a Number) when input a Greek phrase that contains more than one terminal sigma, such as "πιστὸς καὶ ἀληθινός". It is able to identify the value of each letter in that phrase, including all the sigmas, but it is unable to add up the total value:
In the above example, if I replace at least one of the terminal sigmas with a medial sigma, then it is able to compute the correct total value:
