I am working on a chart with the data tracked in a scientific experiment
where the time intervals are not equal.

The first point is at 9 weeks, next at 6 months and tne next at 12 months.
How do I represent the spaces between these points propionate to the time
interval between these points? Please help. I could not find it in the book
-- may be I don't know the exact term that is applied to this.

Thanks for your help