While I'm at it, I tweaked the formula, so the attached:
- uses temperature thresholds (no data validation dropdown to allow free entry of any values) in cells I37 and I38
- plots those thresholds as dotted lines on the chart
- plots green blocks on the chart to show opportunities.
Hopefully this makes it a bit more visual and easy to check it's giving the right results
(Still no 'last n days' adressed!)