How the predict_linear working

Hi Guys,

I was able to use Prometheus predict_linear function to do the prediction for memory.

And I was able to set the time range to now-2d and now + 2d on Grafana.

However, as you can see the image I attached that in my predict linear function, I only predict what the next 6-hour memory would be.

I do not understand is that why the data keep exist for two days. It should not be any data after 6 hours right?

Thanks for your help.