Dynamic chart - Show last 3 data inputs

Hi i want to create a chart that shows the last X data, and i want to be able to select X=2 or X=5 etc.


--A---:---B---:---C---:
Months: Data 1: Data 2:
Jan----:--5---:
Feb---:---0---:
Mar---:---3---:
April---:---2--:

so for chart (Data 1)
i want to be able to select last 3 Data, and it should skip 0 or ignore it and not display it in the graph

thanks!