help to modify the value of a history tag to display it in a graph

I am looking for a way to be able to modify the value of a date range so that it is displayed in a graph, in a table if I could modify the operation but I cannot find how to do it in a graph, the value I am trying to put is this: @(ctim*-1.38)+203.17@
I also tried writing a script but this option doesn’t work for me:
chart.setValue (data [@ (ctim * -1.38) + 203.17 @])
I don’t know if he is declaring it right or wrong.
thanks for your kind help
greetings from Mexico