central moving average
Please add central moving average to trend line options.
Brett Ables commented
There are also about a dozen moving window functions (like cosine bell, hamming window, triangle window) in addition to the classic rectangular window that are useful for constructing filters. A nice Butterworth low pass smoothing filter in Excel would also be great! And every other kind of filter too... basically the v signal processing capabilities of Matlab, Python, LabVIEW, etc.