Using Offset to drive Grafana - PromQL question

[ed.ma...@infinityworks.com]

I'm working on a system that comes under load every Saturday. I'd like to compare the current user metrics for this system with previous Saturdays.

Thus far, i've used the offset modifier to display the min/max values from the previous three saturdays and Grafanas 'Fill to below' feature to represent these in a clear way.

Looks like the below, but with an additional series for 21d:

I'd like to show the values for the previous three Saturdays as a single time series, represented with two queries... 

1. Minimum value seen over the previous 3 Saturdays (offset 7d, offset 14d, offset21d)

2. Maximum value seen over the previous 3 Saturdays (offset 7d, offset 14d, offset21d)

I could then use these to drive the trend graph and improve our dashboards. I've been successful with different offsets, but i've not found a way to combines the time series and select the min/max from that set of time series.

Any help/insight is greatly appreciated!

Thanks

Ed