Currently we don't have nice, out of the box solution for you. We already have received similar feature requests where it would be possible to compare data for given period with data for same period in past with some defined offset. We are looking into various options on how to implement this.
What you can do is - generate data with time offset. Basically you need to create 4 series.
Your single data point would look something like this:
[timestamp, 10, 8, 5, 6]
- data for current Friday (represented with 10).
- data for previous Friday (represented with 8).
- data for even further Friday (represented with 5).
- data for last Friday (represented with 6).
Then configure your TimeChart series like in this example:
Hope it helps.