I have never worked with spreadsheets more than this semester. I usually find myself using spreadsheets 5-6 times per week. They save a lot of time and frustration (except when an order of operations error goes undetected for two hours! ), but recently I had a project in which I needed to interpolate data in an X-Y chart.

I had the discrete X and Y values (in this case current and frequency) plotted on a chart, and I needed to find the value of the frequency at a specific current (in this case current divided by square root of two - which is the "half power" passing through an RLC filter circuit). I thought there would be some easy way to do it - such as the TRACE function on a graphing calculator where the curve is traced until the desired coordinates are found, but after searching the help and online I found no such solution.

After quite a bit of digging, I came across this old post on the MrExcel bulletin board, in which someone needs this exact procedure and the response is "Look for FORECAST function.

The FORECAST function will do this interpolation for you.

=FORECAST(x, known_y's, known_x's)

where x is x-value for which you would like to interpolate and find its corresponding y, and known_y's are from your discrete set of y values, and known_x's are your discrete set of x values. x is a number, and the knowns are ranges of number (cells you select).

I found the function to give very nice results, at least for this application.