This extract "b" only.I want the whole row.

I deleted one accidentally, And I don't know which one. You have good sense of math, the model is nice.

@JackLaVigne It's Amazing.In fact, I get those data from magnetic sensors.The 16 inputs represent magnetic field.And a is the rotation angle of a magnetic stripe, d is the offset.Your answer is very close.{{0, 0}, {10, 0}, {15, 0}, {20, 0}, {25, 0}, {30, 0}} is the exact answer.I will do more exercise.

You mean I must guess the expression of L[x].It's hard to do so.

@aardvark2012 What's Mexican Hat?I'm not a native English speaker.And I don't know how to " finding L as a NonlinearModelFit for t".If I don't use InterpolatingFunction, how to get my function form?

@Coolwater No,data is one of test data.{{...},...}。

I think too much about Union.

It's hard to understand.

I just bother about this way.I need to Normal,then Flatten.