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An error occurred while saving the comment An error occurred while saving the comment Anonymous commentedHere is MS Office advice on lerp
https://support.microsoft.com/enus/help/214096/methodtocalculateinterpolationstepvalueinexcel
DIY basically as I have in my example file/Anonymous shared this idea · 
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An error occurred while saving the comment Anonymous commentedThat's the point, on my system option + click green button doesn't do anything in Excel (or the other Office apps) yet every other app I use (dozens including the entire Adobe CC suite) does what it should.
But double clicking on the titlebar does, so thanks for that (I haven't done that on a mac since System 7 or something when I used a system extension that used to shrink windows into their title bar only!
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Or call it Curve or Interpolation:
=INTERPOLATION (range, [startvalue], [endvalue])
where range is a single column wide or row high range of cells of three or more cells.
start value and end value optional, if not provided then function assumes first cell in range specified is start value and last cell in range is end value for the linear Interpolation.
=CURVE (range, [startvalue], [endvalue], [curveindex])
Where curve index determines the function used to map the interpolation
e.g. 0 = linear
1 = sine
2 = quadratic
3 = cubic
4 = exponential
etc