Dragging cells to fill data - logic behind

[anandsubramanian]

What's the implicit logic used by excel to fill data when we drag the cells?

i.e. I have 43, 124, 20, 312 in four consecutive cells.. when I select them all and drag, it will populate with some values in the fifth cell, sixth cell and so on... How to know what's the logic used by excel?

 

[shg]

Welcome to the board.

It extrapolates of the linear trendline of the first four numbers.