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Hi all,

I am looking to select the starting point of my curve and tare all x,y data to this point.

I tried using the 'findchangepts' function but this doesn't always select the correct point.

Is there an automated function to do this or a way to select the correct point directly from the plot?

T = readtable('sample1.xlsx');

X=T{:,1};

Y=T{:,2};

figure(1)

plot(X, Y)

Chad Greene
on 5 Apr 2021

Perhaps you could find the index of the location where the chage in Y exceeds some critical threshold. You'll have to manually tune the threshold, but consider this case:

X = 1:6;

Y = [0 0 0 1 2 3];

plot(X,Y,'o-')

Find the index of the first location where the change in Y begins:

ind = find(gradient(Y)>0.1,1)

That says the curve begins at the third element. Now I'm not sure what you mean by 'tare', but you can subtract the values at the start of the curve to put the origin at zero, like this:

X = X - X(ind);

Y = Y - Y(ind);

plot(X,Y,'o-')

Or you could delete the first values from the arrays:

X(1:(ind-1)) = [];

Y(1:(ind-1)) = [];

plot(X,Y,'o-')

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