I hope this answers your question for i wasn't given a source or an excerpt so i looked it up.
"When he is first seen by Faustus, he is horrendously ugly. Faustus immediately sends him away and has him reappear in the form of a Franciscan friar. The mere physical appearance of Mephistophilis suggests the ugliness of hell itself."
Technically this is not a math equation so i hope its ok to quote.