Basically, it finds the difference between one cell to another, then able to fill sequence drag plus button For example, Cell A1 has 1, A2 2, A3 3 selecting three A1, A2 & A3 with mouse, then drag right side down plus button, will give sequence like 4,5,6,7,8 until the cursor moved. Same way type Sunday, Monday, Tuesday Select and drag it downside, will give result of Wednesday Thursday like that Hope I have given correct explanation