Linear interpolation problem (15 min data to 10 min data)

Hi All,
First time to post.
I have a data set of water flow (Q) for every 15 min. I need to interpolate the water flow (Q) to every 10 min.


I've looked through several forums and tried a few FORECAST, and OFFSET type formulas, but can't seem to make it work.

Any suggestions for formulas to use? I've attached a sample of the data.
Thanks so much in advance!

I'm not in a position to download your file tonight.

I've found it easiest to break up linear interpolation into 3 steps.

1) Locate the interval containing the desired x value. This can usually be accomplished easily using the =MATCH() function.
2) Use the =INDEX() function to extract the x and y endpoint values for the interval that contains the desired x value.
3) Interpolate to find y and the desired x value. This can be accomplished using the =TREND() function using the results of the four INDEX() functions from step 2.

Thank you MrShorty and shg.

MrShorty I will try to follow your advice, and post back with questions.

Shg- I'm reposting the file with time/date in one column. Looking forward to your response tomorrow.
Thanks again to you both!

Thank you so much! It looks great- but please forgive my lack of excel sophistication...I am unable to copy your LInterp function into other spreadsheets and use if over my whole dataset which is huge.
How do I enable that function in other spreadsheets?

Thank you so much again!