wow, nearly posted this question again as I could not find it!!!
Anyhow, thanks yannK, That's the bit I got to my self with
index=X eventtype="Y" earliest=-90d@w1 latest=+90d@w1 | timechart span=1w max(Z) by Device
but the future values are blank, I want to somehow enter them with some forecast formula as in excel as bmgilmore states below
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