Chart update working when macro executed step by step but not when at full execution

Dear All,

I've got a weird behavior of my macro. The data is x,y,z set of points (scan of a surface); I want to analyze the surface state, so at Y fixed I draw a plot (x,z), i get a x,y scatter plot of the section.
I need to detrend it so i use a 6th degree interpolation. I extract the interpolation from the trendline (TrendLineValue function in VBA) of the grape since LINEST at high degree is not working properly (I know it is dirty but I already spend a lot of time on that).
Then detrend the data, compute root mean square and store it in an array.
And I iterate through different Y (I call them steps).
The problem is between steps, the chart is not updated so trendline equation is not updated so value extracted by TrendLineValue are wrong....
I played around with DoEvents, Wait, application. Calculate but nothing is working....

Please do not mind all code related to FFT, I'm just trying to make this coefficient extraction working.
Thank you for your help.

Here is the file:
gofile.io/?c=q9X9YE

here is the code

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Try using the Application.Ontime method to call your routine. (https://stackoverflow.com/questions/...graph-in-excel)