Try this:
1. In Tools Options | Calculation check Iteration with max change =0
2. Select data range e.g. A1:A30 then Edit Goto Special Blanks
3. With A2 active, type =(A1+A3)/2 and hit Ctrl+Enter (to fill all cells)
4. Copy the range and choose Edit Paste Special Values


"Robert" wrote:

Is there an easy way to interpolate data points, for example if I have 30
cells. The 1st, 12th and the 30th cell have data points only, can excel
populate the empty cells using the giving data points. I can manage this with
a single row of data (small range) but when I run into large data collections
this is to much to for myself to manage. Any thoughts? What I'm looking for
is a more automated method of selecting a horizontal or vertical direction of
interpolation using a varying amount of control points (2d only).

Thanks