Cryptoquip Answer for 09/28/2018

FYIS EYI DZNRE DAGE QNGZS-QNZSCZSQ CIXZLIR FINI ZSXISEIC, FGR EYGE G WZAAREJSI WZAIREJSI?

TODAY’S CLUE: D = F

ANSWER: WHEN THE FIRST FLAT GRAIN-GRINDING DEVICES WERE INVENTED, WAS THAT A MILLSTONE MILESTONE?