# Haw can I calculate the difference between two points in a plot?

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Ahmed Alalawi on 31 Oct 2019
Answered: KALYAN ACHARJYA on 31 Oct 2019
Hi
I would like to get the code for calculating the difference between point A and B in a plot.
I can identify them by looking at the plot, but since I have big data and the points’ position changes every time, it would be nice if I can do them more objectively with codes.
X= time
Y= degrees
I have attached the data and a figure

Try this:
---------------------------------------
plot(...)
[x,y] = ginput(2); % clic on each point
dx = diff(x)
dy = diff(y)
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Enjoy!!!

KALYAN ACHARJYA on 31 Oct 2019
You can do that in number of ways
1. If you know the corresponding x values of A and B,let say d1 and d2 them
idx1=find(x==d1);
idx2=find(x==d2);
result=y(idx1)-y(idx2)
2. If not find the diff of y, where maximum two change occurs, might be A and B, then follow last step of 1.
3. Find Peaks (see the documentation)