add "precision index" to my trend line

Not sure I'm using the right terminology here :-)
Basically what I'd like to achieve is a margin of error (given) to the trend line.
The trend line is achieved using the "add trend line" standard excel function/

I'm specifically refering to the red lines (manually edited with paint in the chart) in the picture in attachment:


Thanks for reading
rs232

Actually the chart is slightly wrong as the red lines should start on the last day of collected data.
Please see this second image in attachment instead.
Cheers

rs232, have you had a look at the different options when inserting a trendline, especially forecast and type polynomial

Yes I did, but:
1) It doesn't seem to be very flexible
2) The positive error (higher red line) goes first below the linear tend line and then above...
3) To do negative error (lower red line) I need to "play with the intercept". It looks similar but it's more guessing then anything else...
4) It still work from the beginning of the data set, where I really need something that underlines the potential error in prediction.

ideally, if I can get the figures of the trendline (not sure how though)
I could create my own lines in the style:

A1 = 77
A2 = (A1*1.001)
A3 = (A2*1.001)
...

+

B1 = 77
B2 = (B1*0.999)
B3 = (B2*0.999)
...

I hope I'm explained myself :-p
Cheers

Sorted, it was possibly too simple to be seen, lol :-D

FIY
I did use the TREND function to work out the linear regression.
From this set of data I just added 2 lines as per my post above (increasing and reducing by 0.001% the value of the previous day, for the period of prediction only.

Cheers
rs232

Glad you found a solution and thanks for posting it here!

could you mark the thread as solved, please?

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