With the same data base but with an old script, I notice that the points were always in the right shape. So the graph has not changed.
After, I have added columns in the data base which are used to make a target and limits in the graph as variables.
I don't use column property with target and USL and LSL limits. .This allows me to have a target that I can change over time. I don't calculate the capability.
So in the end I have the main variable with 2 or 3 other variables for the target and the limits. Under these conditions, it changes the size and shape of the points when I overlap two years.
The graph is OK when I choose only one year.
Is there a solution in my conditions?