Thanks for this information it help me quite a bit, however I noticed that the extendtrend macro provided doesn't work properly unless you are searching with a bucket span of 1 day.
I used the following macro which gave me a more accurate picture.
[lineartrendextend(3)]
args = x, y, end
description = Extends lineartrend(2), x and y should match the args provided to lineartrend, end should be the number of days into the future you would like to extend the trend.
definition = append [ gentimes start=1 end=$end$ |rename starttime as _time | fields _time] |eventstats values(yintercept) as yintercept, values(slope) as slope, values(numevents) as numevents | eval newY=(yintercept + (slope * _time)) | fields _time, $y$, newY
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