During my PhD, one thing I found myself doing time and time again was interpolating X,Y data points. For example, I often digitsed graphs from old papers, and the X coordinates of the resulting points were always some weird values (corresponding to whatever pixel the digitising program detected). Other uses were where I had, for example, a calibration file for a spectrometer which had data points in 5nm steps, but my spectra were in 1nm steps.
This Excel file performs linear interpolation of a series of input X,Y data points and outputs a list of interpolated Y values at each entry in a list of X values. For example, if you run it as it is, it has input data (0,0) (2,4) (4,16) (6,36) (8,64) (10,100). We want to know the interpolated values at X values of 1,2,3,4, and it can calculate these. You'll get the idea! It's maybe not the quickest, but it does the job.
Download the spreadsheet here.