Miller’s error was to spiritualize the 2,300 days described in Daniel 8:14 as years and then figure them into a chronology he developed from scripture that yielded for him the October 22nd, 1844 date. Those 2,300 years really speak to the time Antiochus IV persecuted the Jewish nation for 6 years and four months from 17o AD to 164 AD. The cleansing of the temple referred to by Daniel was when the sacrifices were restored by the Maccabees. We know it as Hanukkah.
Miller ignored Acts 1:7, where Christ specifically told His disciples (and us) that it is not for us to know the times or the seasons. Those things are left only to the Lord.