In an equation screener, what's the difference between TTM and 1 Calendar Year Ago?

1 Calendar Year Ago indicates what the value would be at the end of the previous calendar year, whereas TTM (trailing twelve months) corresponds with the value exactly 12 months earlier. For example, if today is 9/25/15, ‘1 Calendar Year Ago’ will use the values from 12/31/14, whereas TTM would look at the values from 9/25/14.